Chapter 7 Practice Problems (Practice – no credit) Due: 11:59pm on Friday, March 14, 2014 You will receive no credit for items you complete after the assignment is due. Grading Policy A Book on a Table A book weighing 5 N rests on top of a table. Part A A downward force of magnitude 5 N is exerted on the book by the force of ANSWER: Part B An upward force of magnitude _____ is exerted on the _____ by the table. the table gravity inertia . ANSWER: Part C Do the downward force in Part A and the upward force in Part B constitute a 3rd law pair? You did not open hints for this part. ANSWER: Part D The reaction to the force in Part A is a force of magnitude _____, exerted on the _____ by the _____. Its direction is _____ . You did not open hints for this part. ANSWER: 6 N / table 5 N / table 5 N / book 6 N / book yes no Part E The reaction to the force in Part B is a force of magnitude _____, exerted on the _____ by the _____. Its direction is _____. ANSWER: Part F Which of Newton’s laws dictates that the forces in Parts A and B are equal and opposite? ANSWER: Part G Which of Newton’s laws dictates that the forces in Parts B and E are equal and opposite? ANSWER: 5 N / earth / book / upward 5 N / book / table / upward 5 N / book / earth / upward 5 N / earth / book / downward 5 N / table / book / upward 5 N / table / earth / upward 5 N / book / table / upward 5 N / table / book / downward 5 N / earth / book / downward Newton’s 1st or 2nd law Newton’s 3rd law Blocks in an Elevator Ranking Task Three blocks are stacked on top of each other inside an elevator as shown in the figure. Answer the following questions with reference to the eight forces defined as follows. the force of the 3 block on the 2 block, , the force of the 2 block on the 3 block, , the force of the 3 block on the 1 block, , the force of the 1 block on the 3 block, , the force of the 2 block on the 1 block, , the force of the 1 block on the 2 block, , the force of the 1 block on the floor, , and the force of the floor on the 1 block, . Part A Assume the elevator is at rest. Rank the magnitude of the forces. Rank from largest to smallest. To rank items as equivalent, overlap them. You did not open hints for this part. ANSWER: Newton’s 1st or 2nd law Newton’s 3rd law kg kg F3 on 2 kg kg F2 on 3 kg kg F3 on 1 kg kg F1 on 3 kg kg F2 on 1 kg kg F1 on 2 kg F1 on floor kg Ffloor on 1 Part B This question will be shown after you complete previous question(s). Newton’s 3rd Law Discussed Learning Goal: To understand Newton’s 3rd law, which states that a physical interaction always generates a pair of forces on the two interacting bodies. In Principia, Newton wrote: To every action there is always opposed an equal reaction: or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. (translation by Cajori) The phrase after the colon (often omitted from textbooks) makes it clear that this is a statement about the nature of force. The central idea is that physical interactions (e.g., due to gravity, bodies touching, or electric forces) cause forces to arise between pairs of bodies. Each pairwise interaction produces a pair of opposite forces, one acting on each body. In summary, each physical interaction between two bodies generates a pair of forces. Whatever the physical cause of the interaction, the force on body A from body B is equal in magnitude and opposite in direction to the force on body B from body A. Incidentally, Newton states that the word “action” denotes both (a) the force due to an interaction and (b) the changes in momentum that it imparts to the two interacting bodies. If you haven’t learned about momentum, don’t worry; for now this is just a statement about the origin of forces. Mark each of the following statements as true or false. If a statement refers to “two bodies” interacting via some force, you are not to assume that these two bodies have the same mass. Part A Every force has one and only one 3rd law pair force. ANSWER: Part B The two forces in each pair act in opposite directions. ANSWER: Part C The two forces in each pair can either both act on the same body or they can act on different bodies. ANSWER: true false true false Part D The two forces in each pair may have different physical origins (for instance, one of the forces could be due to gravity, and its pair force could be due to friction or electric charge). ANSWER: Part E The two forces of a 3rd law pair always act on different bodies. ANSWER: Part F Given that two bodies interact via some force, the accelerations of these two bodies have the same magnitude but opposite directions. (Assume no other forces act on either body.) You did not open hints for this part. ANSWER: true false true false true false Part G According to Newton’s 3rd law, the force on the (smaller) moon due to the (larger) earth is ANSWER: Pulling Three Blocks Three identical blocks connected by ideal strings are being pulled along a horizontal frictionless surface by a horizontal force . The magnitude of the tension in the string between blocks B and C is = 3.00 . Assume that each block has mass = 0.400 . true false greater in magnitude and antiparallel to the force on the earth due to the moon. greater in magnitude and parallel to the force on the earth due to the moon. equal in magnitude but antiparallel to the force on the earth due to the moon. equal in magnitude and parallel to the force on the earth due to the moon. smaller in magnitude and antiparallel to the force on the earth due to the moon. smaller in magnitude and parallel to the force on the earth due to the moon. F T N m kg Part A What is the magnitude of the force? Express your answer numerically in newtons. You did not open hints for this part. ANSWER: Part B What is the tension in the string between block A and block B? Express your answer numerically in newtons You did not open hints for this part. ANSWER: Pulling Two Blocks In the situation shown in the figure, a person is pulling with a constant, nonzero force on string 1, which is attached to block A. Block A is also attached to block B via string 2, as shown. For this problem, assume that neither string stretches and that friction is negligible. Both blocks have finite (nonzero) mass. F F = N TAB TAB = N F Part A Which one of the following statements correctly descibes the relationship between the accelerations of blocks A and B? You did not open hints for this part. ANSWER: Part B How does the magnitude of the tension in string 1, , compare with the tension in string 2, ? You did not open hints for this part. Block A has a larger acceleration than block B. Block B has a larger acceleration than block A. Both blocks have the same acceleration. More information is needed to determine the relationship between the accelerations. T1 T2 ANSWER: Tension in a Massless Rope Learning Goal: To understand the concept of tension and the relationship between tension and force. This problem introduces the concept of tension. The example is a rope, oriented vertically, that is being pulled from both ends. Let and (with u for up and d for down) represent the magnitude of the forces acting on the top and bottom of the rope, respectively. Assume that the rope is massless, so that its weight is negligible compared with the tension. (This is not a ridiculous approximation–modern rope materials such as Kevlar can carry tensions thousands of times greater than the weight of tens of meters of such rope.) Consider the three sections of rope labeled a, b, and c in the figure. At point 1, a downward force of magnitude acts on section a. At point 1, an upward force of magnitude acts on section b. At point 1, the tension in the rope is . At point 2, a downward force of magnitude acts on section b. At point 2, an upward force of magnitude acts on section c. At point 2, the tension in the rope is . Assume, too, that the rope is at equilibrium. Part A What is the magnitude of the downward force on section a? Express your answer in terms of the tension . ANSWER: More information is needed to determine the relationship between and . T1 > T2 T1 = T2 T1 < T2 T1 T2 Fu Fd Fad Fbu T1 Fbd Fcu T2 Fad T1 Part B What is the magnitude of the upward force on section b? Express your answer in terms of the tension . ANSWER: Part C The magnitude of the upward force on c, , and the magnitude of the downward force on b, , are equal because of which of Newton's laws? ANSWER: Part D The magnitude of the force is ____ . ANSWER: Fad = Fbu T1 Fbu = Fcu Fbd 1st 2nd 3rd Fbu Fbd Part E Now consider the forces on the ends of the rope. What is the relationship between the magnitudes of these two forces? You did not open hints for this part. ANSWER: Part F The ends of a massless rope are attached to two stationary objects (e.g., two trees or two cars) so that the rope makes a straight line. For this situation, which of the following statements are true? Check all that apply. ANSWER: less than greater than equal to Fu > Fd Fu = Fd Fu < Fd The tension in the rope is everywhere the same. The magnitudes of the forces exerted on the two objects by the rope are the same. The forces exerted on the two objects by the rope must be in opposite directions. The forces exerted on the two objects by the rope must be in the direction of the rope. Two Hanging Masses Two blocks with masses and hang one under the other. For this problem, take the positive direction to be upward, and use for the magnitude of the acceleration due to gravity. Case 1: Blocks at rest For Parts A and B assume the blocks are at rest. Part A Find , the tension in the lower rope. Express your answer in terms of some or all of the variables , , and . You did not open hints for this part. ANSWER: M1 M2 g T2 M1 M2 g Part B Find , the tension in the upper rope. Express your answer in terms of some or all of the variables , , and . You did not open hints for this part. ANSWER: Case 2: Accelerating blocks For Parts C and D the blocks are now accelerating upward (due to the tension in the strings) with acceleration of magnitude . Part C Find , the tension in the lower rope. Express your answer in terms of some or all of the variables , , , and . You did not open hints for this part. ANSWER: T2 = T1 M1 M2 g T1 = a T2 M1 M2 a g Part D Find , the tension in the upper rope. Express your answer in terms of some or all of the variables , , , and . You did not open hints for this part. ANSWER: Video Tutor: Suspended Balls: Which String Breaks? First, launch the video below. You will be asked to use your knowledge of physics to predict the outcome of an experiment. Then, close the video window and answer the question at right. You can watch the video again at any point. T2 = T1 M1 M2 a g T1 = Part A A heavy crate is attached to the wall by a light rope, as shown in the figure. Another rope hangs off the opposite edge of the box. If you slowly increase the force on the free rope by pulling on it in a horizontal direction, which rope will break? Ignore friction and the mass of the ropes. You did not open hints for this part. ANSWER: Score Summary: Your score on this assignment is 0%. You received 0 out of a possible total of 0 points. The rope attached to the wall will break. The rope that you are pulling on will break. Both ropes are equally likely to break.

Chapter 7 Practice Problems (Practice – no credit) Due: 11:59pm on Friday, March 14, 2014 You will receive no credit for items you complete after the assignment is due. Grading Policy A Book on a Table A book weighing 5 N rests on top of a table. Part A A downward force of magnitude 5 N is exerted on the book by the force of ANSWER: Part B An upward force of magnitude _____ is exerted on the _____ by the table. the table gravity inertia . ANSWER: Part C Do the downward force in Part A and the upward force in Part B constitute a 3rd law pair? You did not open hints for this part. ANSWER: Part D The reaction to the force in Part A is a force of magnitude _____, exerted on the _____ by the _____. Its direction is _____ . You did not open hints for this part. ANSWER: 6 N / table 5 N / table 5 N / book 6 N / book yes no Part E The reaction to the force in Part B is a force of magnitude _____, exerted on the _____ by the _____. Its direction is _____. ANSWER: Part F Which of Newton’s laws dictates that the forces in Parts A and B are equal and opposite? ANSWER: Part G Which of Newton’s laws dictates that the forces in Parts B and E are equal and opposite? ANSWER: 5 N / earth / book / upward 5 N / book / table / upward 5 N / book / earth / upward 5 N / earth / book / downward 5 N / table / book / upward 5 N / table / earth / upward 5 N / book / table / upward 5 N / table / book / downward 5 N / earth / book / downward Newton’s 1st or 2nd law Newton’s 3rd law Blocks in an Elevator Ranking Task Three blocks are stacked on top of each other inside an elevator as shown in the figure. Answer the following questions with reference to the eight forces defined as follows. the force of the 3 block on the 2 block, , the force of the 2 block on the 3 block, , the force of the 3 block on the 1 block, , the force of the 1 block on the 3 block, , the force of the 2 block on the 1 block, , the force of the 1 block on the 2 block, , the force of the 1 block on the floor, , and the force of the floor on the 1 block, . Part A Assume the elevator is at rest. Rank the magnitude of the forces. Rank from largest to smallest. To rank items as equivalent, overlap them. You did not open hints for this part. ANSWER: Newton’s 1st or 2nd law Newton’s 3rd law kg kg F3 on 2 kg kg F2 on 3 kg kg F3 on 1 kg kg F1 on 3 kg kg F2 on 1 kg kg F1 on 2 kg F1 on floor kg Ffloor on 1 Part B This question will be shown after you complete previous question(s). Newton’s 3rd Law Discussed Learning Goal: To understand Newton’s 3rd law, which states that a physical interaction always generates a pair of forces on the two interacting bodies. In Principia, Newton wrote: To every action there is always opposed an equal reaction: or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. (translation by Cajori) The phrase after the colon (often omitted from textbooks) makes it clear that this is a statement about the nature of force. The central idea is that physical interactions (e.g., due to gravity, bodies touching, or electric forces) cause forces to arise between pairs of bodies. Each pairwise interaction produces a pair of opposite forces, one acting on each body. In summary, each physical interaction between two bodies generates a pair of forces. Whatever the physical cause of the interaction, the force on body A from body B is equal in magnitude and opposite in direction to the force on body B from body A. Incidentally, Newton states that the word “action” denotes both (a) the force due to an interaction and (b) the changes in momentum that it imparts to the two interacting bodies. If you haven’t learned about momentum, don’t worry; for now this is just a statement about the origin of forces. Mark each of the following statements as true or false. If a statement refers to “two bodies” interacting via some force, you are not to assume that these two bodies have the same mass. Part A Every force has one and only one 3rd law pair force. ANSWER: Part B The two forces in each pair act in opposite directions. ANSWER: Part C The two forces in each pair can either both act on the same body or they can act on different bodies. ANSWER: true false true false Part D The two forces in each pair may have different physical origins (for instance, one of the forces could be due to gravity, and its pair force could be due to friction or electric charge). ANSWER: Part E The two forces of a 3rd law pair always act on different bodies. ANSWER: Part F Given that two bodies interact via some force, the accelerations of these two bodies have the same magnitude but opposite directions. (Assume no other forces act on either body.) You did not open hints for this part. ANSWER: true false true false true false Part G According to Newton’s 3rd law, the force on the (smaller) moon due to the (larger) earth is ANSWER: Pulling Three Blocks Three identical blocks connected by ideal strings are being pulled along a horizontal frictionless surface by a horizontal force . The magnitude of the tension in the string between blocks B and C is = 3.00 . Assume that each block has mass = 0.400 . true false greater in magnitude and antiparallel to the force on the earth due to the moon. greater in magnitude and parallel to the force on the earth due to the moon. equal in magnitude but antiparallel to the force on the earth due to the moon. equal in magnitude and parallel to the force on the earth due to the moon. smaller in magnitude and antiparallel to the force on the earth due to the moon. smaller in magnitude and parallel to the force on the earth due to the moon. F T N m kg Part A What is the magnitude of the force? Express your answer numerically in newtons. You did not open hints for this part. ANSWER: Part B What is the tension in the string between block A and block B? Express your answer numerically in newtons You did not open hints for this part. ANSWER: Pulling Two Blocks In the situation shown in the figure, a person is pulling with a constant, nonzero force on string 1, which is attached to block A. Block A is also attached to block B via string 2, as shown. For this problem, assume that neither string stretches and that friction is negligible. Both blocks have finite (nonzero) mass. F F = N TAB TAB = N F Part A Which one of the following statements correctly descibes the relationship between the accelerations of blocks A and B? You did not open hints for this part. ANSWER: Part B How does the magnitude of the tension in string 1, , compare with the tension in string 2, ? You did not open hints for this part. Block A has a larger acceleration than block B. Block B has a larger acceleration than block A. Both blocks have the same acceleration. More information is needed to determine the relationship between the accelerations. T1 T2 ANSWER: Tension in a Massless Rope Learning Goal: To understand the concept of tension and the relationship between tension and force. This problem introduces the concept of tension. The example is a rope, oriented vertically, that is being pulled from both ends. Let and (with u for up and d for down) represent the magnitude of the forces acting on the top and bottom of the rope, respectively. Assume that the rope is massless, so that its weight is negligible compared with the tension. (This is not a ridiculous approximation–modern rope materials such as Kevlar can carry tensions thousands of times greater than the weight of tens of meters of such rope.) Consider the three sections of rope labeled a, b, and c in the figure. At point 1, a downward force of magnitude acts on section a. At point 1, an upward force of magnitude acts on section b. At point 1, the tension in the rope is . At point 2, a downward force of magnitude acts on section b. At point 2, an upward force of magnitude acts on section c. At point 2, the tension in the rope is . Assume, too, that the rope is at equilibrium. Part A What is the magnitude of the downward force on section a? Express your answer in terms of the tension . ANSWER: More information is needed to determine the relationship between and . T1 > T2 T1 = T2 T1 < T2 T1 T2 Fu Fd Fad Fbu T1 Fbd Fcu T2 Fad T1 Part B What is the magnitude of the upward force on section b? Express your answer in terms of the tension . ANSWER: Part C The magnitude of the upward force on c, , and the magnitude of the downward force on b, , are equal because of which of Newton's laws? ANSWER: Part D The magnitude of the force is ____ . ANSWER: Fad = Fbu T1 Fbu = Fcu Fbd 1st 2nd 3rd Fbu Fbd Part E Now consider the forces on the ends of the rope. What is the relationship between the magnitudes of these two forces? You did not open hints for this part. ANSWER: Part F The ends of a massless rope are attached to two stationary objects (e.g., two trees or two cars) so that the rope makes a straight line. For this situation, which of the following statements are true? Check all that apply. ANSWER: less than greater than equal to Fu > Fd Fu = Fd Fu < Fd The tension in the rope is everywhere the same. The magnitudes of the forces exerted on the two objects by the rope are the same. The forces exerted on the two objects by the rope must be in opposite directions. The forces exerted on the two objects by the rope must be in the direction of the rope. Two Hanging Masses Two blocks with masses and hang one under the other. For this problem, take the positive direction to be upward, and use for the magnitude of the acceleration due to gravity. Case 1: Blocks at rest For Parts A and B assume the blocks are at rest. Part A Find , the tension in the lower rope. Express your answer in terms of some or all of the variables , , and . You did not open hints for this part. ANSWER: M1 M2 g T2 M1 M2 g Part B Find , the tension in the upper rope. Express your answer in terms of some or all of the variables , , and . You did not open hints for this part. ANSWER: Case 2: Accelerating blocks For Parts C and D the blocks are now accelerating upward (due to the tension in the strings) with acceleration of magnitude . Part C Find , the tension in the lower rope. Express your answer in terms of some or all of the variables , , , and . You did not open hints for this part. ANSWER: T2 = T1 M1 M2 g T1 = a T2 M1 M2 a g Part D Find , the tension in the upper rope. Express your answer in terms of some or all of the variables , , , and . You did not open hints for this part. ANSWER: Video Tutor: Suspended Balls: Which String Breaks? First, launch the video below. You will be asked to use your knowledge of physics to predict the outcome of an experiment. Then, close the video window and answer the question at right. You can watch the video again at any point. T2 = T1 M1 M2 a g T1 = Part A A heavy crate is attached to the wall by a light rope, as shown in the figure. Another rope hangs off the opposite edge of the box. If you slowly increase the force on the free rope by pulling on it in a horizontal direction, which rope will break? Ignore friction and the mass of the ropes. You did not open hints for this part. ANSWER: Score Summary: Your score on this assignment is 0%. You received 0 out of a possible total of 0 points. The rope attached to the wall will break. The rope that you are pulling on will break. Both ropes are equally likely to break.

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1) If a superalloy jet engine is heated so that its length in each direction expands by 1%, what is its percentage change in volume (assume it is roughly cubic)? Hint: Calculate its volume before and after heating, assuming that its length, height, and width are the same, i.e., a cubic engine. 2) Calculate the density of Al in g/cm3, given that it forms an FCC crystal structure with an atomic radius of 0.143 nm (10-7 cm) and a mass of 27 g/mole. Avogadro’s number is 6.02 x 1023 atoms/mole. Hint: calculate the number of atoms in each cell carefully. 3) Calculate the vacancy concentration in aluminum at 50%, 70%, and 90% of TMP=923 K. Gvf = 0.66 eV, and k = 8.62 x 10-5 eV/K. Calculate ln (nv/N) and 1/T, and plot on a linear scale (hint: should be a straight line). 4) a) If the vacancy concentration in Cu is measured to be 10-5 at 1300K (near its melting point), what is Evf? (assume the pre-exponential factor is 1; ie, nv/N = exp (-Evf/kT) b) What would be the concentration at 650 K? 5) Determine the largest size of an interstitial hole in FCC Fe. RFe = 0.124 nm. Would a C atom sit in an interstitial or substitutional site (rC = 0.077 nm)?

1) If a superalloy jet engine is heated so that its length in each direction expands by 1%, what is its percentage change in volume (assume it is roughly cubic)? Hint: Calculate its volume before and after heating, assuming that its length, height, and width are the same, i.e., a cubic engine. 2) Calculate the density of Al in g/cm3, given that it forms an FCC crystal structure with an atomic radius of 0.143 nm (10-7 cm) and a mass of 27 g/mole. Avogadro’s number is 6.02 x 1023 atoms/mole. Hint: calculate the number of atoms in each cell carefully. 3) Calculate the vacancy concentration in aluminum at 50%, 70%, and 90% of TMP=923 K. Gvf = 0.66 eV, and k = 8.62 x 10-5 eV/K. Calculate ln (nv/N) and 1/T, and plot on a linear scale (hint: should be a straight line). 4) a) If the vacancy concentration in Cu is measured to be 10-5 at 1300K (near its melting point), what is Evf? (assume the pre-exponential factor is 1; ie, nv/N = exp (-Evf/kT) b) What would be the concentration at 650 K? 5) Determine the largest size of an interstitial hole in FCC Fe. RFe = 0.124 nm. Would a C atom sit in an interstitial or substitutional site (rC = 0.077 nm)?

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5 { GRAVITATION Last Updated: July 16, 2012 Problem List 5.1 Total mass of a shell 5.2 Tunnel through the moon 5.3 Gravitational eld above the center of a thin hoop 5.4 Gravitational force near a metal-cored planet surrounded by a gaseous cloud 5.5 Sphere with linearly increasing mass density 5.6 Jumping o Vesta 5.7 Gravitational force between two massive rods 5.8 Potential energy { Check your answer! 5.9 Ways of solving gravitational problems 5.10 Rod with linearly increasing mass density 5.11 Sphere with constant internal gravitational eld 5.12 Throwing a rock o the moon These problems are licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Un- ported License. Please share and/or modify. Back to Problem List 1 5 { GRAVITATION Last Updated: July 16, 2012 5.1 Total mass of a shell Given: Marino { Fall 2011 Consider a spherical shell that extends from r = R to r = 2R with a non-uniform density (r) = 0r. What is the total mass of the shell? Back to Problem List 2 5 { GRAVITATION Last Updated: July 16, 2012 5.2 Tunnel through the moon Given: Marino { Fall 2011 Imagine that NASA digs a straight tunnel through the center of the moon (see gure) to access the Moon’s 3He deposits. An astronaut places a rock in the tunnel at the surface of the moon, and releases it (from rest). Show that the rock obeys the force law for a mass connected to a spring. What is the spring constant? Find the oscillation period for this motion if you assume that Moon has a mass of 7.351022 kg and a radius of 1.74106 m. Assume the moon’s density is uniform throughout its volume, and ignore the moon’s rotation. Given: Pollock { Spring 2011 Imagine (in a parallel universe of unlimited budgets) that NASA digs a straight tunnel through the center of the moon (see gure). A robot place a rock in the tunnel at position r = r0 from the center of the moon, and releases it (from rest). Use Newton’s second law to write the equation of motion of the rock and solve for r(t). Explain in words the rock’s motion. Does the rock return to its initial position at any later time? If so, how long does it takes to return to it? (Give a formula, and a number.) Assume the moon’s density is uniform throughout its volume, and ignore the moon’s rotation. Given: Pollock { Spring 2012 Now lets consider our (real) planet Earth, with total mass M and radius R which we will approximate as a uniform mass density, (r) = 0. (a) Neglecting rotational and frictional e ects, show that a particle dropped into a hole drilled straight through the center of the earth all the way to the far side will oscillate between the two endpoints. (Hint: you will need to set up, and solve, an ODE for the motion) (b) Find the period of the oscillation of this motion. Get a number (in minutes) as a nal result, using data for the earth’s size and mass. (How does that compare to ying to Perth and back?!) Extra Credit: OK, even with unlimited budgets, digging a tunnel through the center of the earth is preposterous. But, suppose instead that the tunnel is a straight-line \chord” through the earth, say directly from New York to Los Angeles. Show that your nal answer for the time taken does not depend on the location of that chord! This is rather remarkable – look again at the time for a free-fall trip (no energy required, except perhaps to compensate for friction) How long would that trip take? Could this work?! Back to Problem List 3 5 { GRAVITATION Last Updated: July 16, 2012 5.3 Gravitational eld above the center of a thin hoop Given: Pollock { Spring 2011, Spring 2012 Consider a very (in nitesimally!) thin but massive loop, radius R (total mass M), centered around the origin, sitting in the x-y plane. Assume it has a uniform linear mass density  (which has units of kg/m) all around it. (So, it’s like a skinny donut that is mostly hole, centered around the z-axis) (a) What is  in terms of M and R? What is the direction of the gravitational eld generated by this mass distribution at a point in space a distance z above the center of the donut, i.e. at (0; 0; z) Explain your reasoning for the direction carefully, try not to simply \wave your hands.” (The answer is extremely intuitive, but can you justify that it is correct?) (b) Compute the gravitational eld, ~g, at the point (0; 0; z) by directly integrating Newton’s law of gravity, summing over all in nitesimal \chunks” of mass along the loop. (c) Compute the gravitational potential at the point (0; 0; z) by directly integrating ?Gdm=r, sum- ming over all in nitesimal \chunks” dm along the loop. Then, take the z-component of the gradient of this potential to check that you agree with your result from the previous part. (d) In the two separate limits z << R and z >> R, Taylor expand your g- eld (in the z-direction)out only to the rst non-zero term, and convince us that both limits make good physical sense. (e) Can you use Gauss’ law to gure out the gravitational potential at the point (0; 0; z)? (If so, do it and check your previous answers. If not, why not?) Extra credit: If you place a small mass a small distance z away from the center, use your Taylor limit for z << R above to write a simple ODE for the equation of motion. Solve it, and discuss the motion Back to Problem List 4 5 { GRAVITATION Last Updated: July 16, 2012 5.4 Gravitational force near a metal-cored planet surrounded by a gaseous cloud Given: Pollock { Spring 2011 Jupiter is composed of a dense spherical core (of liquid metallic hydrogen!) of radius Rc. It is sur- rounded by a spherical cloud of gaseous hydrogen of radius Rg, where Rg > Rc. Let’s assume that the core is of uniform density c and the gaseous cloud is also of uniform density g. What is the gravitational force on an object of mass m that is located at a radius r from the center of Jupiter? Note that you must consider the cases where the object is inside the core, within the gas layer, and outside of the planet. Back to Problem List 5 5 { GRAVITATION Last Updated: July 16, 2012 5.5 Sphere with linearly increasing mass density Given: Pollock { Spring 2011 A planet of mass M and radius R has a nonuniform density that varies with r, the distance from the center according to  = Ar for 0  r  R. (a) What is the constant A in terms of M and R? Does this density pro le strike you as physically plausible, or is just designed as a mathematical exercise? (Brie y, explain) (b) Determine the gravitational force on a satellite of mass m orbiting this planet. In words, please outline the method you plan to use for your solution. (Use the easiest method you can come up with!) In your calculation, you will need to argue that the magnitude of ~g(r; ; ) depends only on r. Be very explicit about this – how do you know that it doesn’t, in fact, depend on  or ? (c) Determine the gravitational force felt by a rock of mass m inside the planet, located at radius r < R. (If the method you use is di erent than in part b, explain why you switched. If not, just proceed!) Explicitly check your result for this part by considering the limits r ! 0 and r ! R. Back to Problem List 6 5 { GRAVITATION Last Updated: July 16, 2012 5.6 Jumping o Vesta Given: Pollock { Spring 2011 You are stranded on the surface of the asteroid Vesta. If the mass of the asteroid is M and its radius is R, how fast would you have to jump o its surface to be able to escape from its gravitational eld? (Your estimate should be based on parameters that characterize the asteroid, not parameters that describe your jumping ability.) Given your formula, look up the approximate mass and radius of the asteroid Vesta 3 and determine a numerical value of the escape velocity. Could you escape in this way? (Brie y, explain) If so, roughly how big in radius is the maximum the asteroid could be, for you to still escape this way? If not, estimate how much smaller an asteroid you would need, to escape from it in this way? Figure 1: Back to Problem List 7 5 { GRAVITATION Last Updated: July 16, 2012 5.7 Gravitational force between two massive rods Given: Pollock { Spring 2011 Consider two identical uniform rods of length L and mass m lying along the same line and having their closest points separated by a distance d as shown in the gure (a) Calculate the mutual force between these rods, both its direction and magnitude. (b) Now do several checks. First, make sure the units worked out (!) The, nd the magnitude of the force in the limit L ! 0. What do you expect? Brie y, discuss. Lastly, nd the magnitude of the force in the limit d ! 1 ? Again, is it what you expect? Brie y, discuss. Figure 2: Given: Pollock { Spring 2012 Determining the gravitational force between two rods: (a) Consider a thin, uniform rod of mass m and length L (and negligible other dimensions) lying on the x axis (from x=-L to 0), as shown in g 1a. Derive a formula for the gravitational eld \g" at any arbitrary point x to the right of the origin (but still on the x-axis!) due to this rod. (b) Now suppose a second rod of length L and mass m sits on the x axis as shown in g 1b, with the left edge a distance \d" away. Calculate the mutual gravitational force between these rods. (c) Let's do some checks! Show that the units work out in parts a and b. Find the magnitude of the force in part a, in the limit x >> L: What do you expect? Brie y, discuss! Finally, verify that your answer to part b gives what you expect in the limit d >> L. ( Hint: This is a bit harder! You need to consistently expand everything to second order, not just rst, because of some interesting cancellations) Fig 1a Fig 1b L m +x x=0 L x=0 x=d m Fig 1a Fig 1b L m +x x=0 L +x x=0 x=d L m m Back to Problem List 8 5 { GRAVITATION Last Updated: July 16, 2012 5.8 Potential energy { Check your answer! Given: Pollock { Spring 2011 On the last exam, we had a problem with a at ring, uniform mass per unit area of , inner radius of R, outer radius of 2R. A satellite (mass m) sat a distance z above the center of the ring. We asked for the gravitational potential energy, and the answer was U(z) = ?2Gm( p 4R2 + z2 ? p R2 + z2) (1) (a) If you are far from the disk (on the z axis), what do you expect for the formula for U(z)? (Don’t say \0″ – as usual, we want the functional form of U(z) as you move far away. Also, explicitly state what we mean by \far away”. (Please don’t compare something with units to something without units!) (b) Show explicitly that the formula above does indeed give precisely the functional dependence you expect. Back to Problem List 9 5 { GRAVITATION Last Updated: July 16, 2012 5.9 Ways of solving gravitational problems Given: Pollock { Spring 2011, Spring 2012 Infinite cylinder ρ=cr x z (a) Half-infinite line mass, uniform linear mass density, λ x (b) R z  P Figure 3: (a) An in nite cylinder of radius R centered on the z-axis, with non-uniform volume mass density  = cr, where r is the radius in cylindrical coordinates. (b) A half-in nite line of mass on the x-axis extending from x = 0 to x = +1, with uniform linear mass density . There are two general methods we use to solve gravitational problems (i.e. nd ~g given some distribution of mass). (a) Describe these two methods. We claim one of these methods is easiest to solve for ~g of mass distribution (a) above, and the other method is easiest to solve for ~g of the mass distribution (b) above. Which method goes with which mass distribution? Please justify your answer. (b) Find ~g of the mass distribution (a) above for any arbitrary point outside the cylinder. (c) Find the x component of the gravitational acceleration, gx, generated by the mass distribution labeled (b) above, at a point P a given distance z up the positive z-axis (as shown). Back to Problem List 10 5 { GRAVITATION Last Updated: July 16, 2012 5.10 Rod with linearly increasing mass density Given: Pollock { Spring 2012 Consider a very (in nitesimally!) thin but massive rod, length L (total mass M), centered around the origin, sitting along the x-axis. (So the left end is at (-L/2, 0,0) and the right end is at (+L/2,0,0) Assume the mass density  (which has units of kg/m)is not uniform, but instead varies linearly with distance from the origin, (x) = cjxj. (a) What is that constant \c” in terms of M and L? What is the direction of the gravitational eld generated by this mass distribution at a point in space a distance z above the center of the rod, i.e. at (0; 0; z) Explain your reasoning for the direction carefully, try not to simply \wave your hands.” (The answer is extremely intuitive, but can you justify that it is correct?) (b) Compute the gravitational eld, ~g, at the point (0; 0; z) by directly integrating Newton’s law of gravity, summing over all in nitesimal \chunks” of mass along the rod. (c) Compute the gravitational potential at the point (0; 0; z) by directly integrating ?Gdm=r, sum- ming over all in nitesimal \chunks” dm along the rod. Then, take the z-component of the gradient of this potential to check that you agree with your result from the previous part. (d) In the limit of large z what do you expect for the functional form for gravitational potential? (Hint: Don’t just say it goes to zero! It’s a rod of mass M, when you’re far away what does it look like? How does it go to zero?) What does \large z” mean here? Use the binomial (or Taylor) expansion to verify that your formula does indeed give exactly what you expect. (Hint: you cannot Taylor expand in something BIG, you have to Taylor expand in something small.) (e) Can you use Gauss’ law to gure out the gravitational potential at the point (0; 0; z)? (If so, do it and check your previous answers. If not, why not?) Back to Problem List 11 5 { GRAVITATION Last Updated: July 16, 2012 5.11 Sphere with constant internal gravitational eld Given: Pollock { Spring 2012 (a) Imagine a planet of total mass M and radius R which has a nonuniform mass density that varies just with r, the distance from the center. For this (admittedly very unusual!) planet, suppose the gravitational eld strength inside the planet turns out to be independent of the radial distance within the sphere. Find the function describing the mass density  = (r) of this planet. (Your nal answer should be written in terms of the given constants.) (b) Now, determine the gravitational force on a satellite of mass m orbiting this planet at distance r > R. (Use the easiest method you can come up with!) Explain your work in words as well as formulas. For instance, in your calculation, you will need to argue that the magnitude of ~g(r; ; ) depends only on r. Be explicit about this – how do you know that it doesn’t, in fact, depend on  or ? (c) As a nal check, explicitly show that your solutions inside and outside the planet (parts a and b) are consistent when r = R. Please also comment on whether this density pro le strikes you as physically plausible, or is it just designed as a mathematical exercise? Defend your reasoning. Back to Problem List 12 5 { GRAVITATION Last Updated: July 16, 2012 5.12 Throwing a rock o the moon Given: Pollock { Spring 2012 Assuming that asteroids have roughly the same mass density as the moon, make an estimate of the largest asteroid that an astronaut could be standing on, and still have a chance of throwing a small object (with their arms, no machinery!) so that it completely escapes the asteroid’s gravitational eld. (This minimum speed is called \escape velocity”) Is the size you computed typical for asteroids in our solar system? Back to Problem List 13

5 { GRAVITATION Last Updated: July 16, 2012 Problem List 5.1 Total mass of a shell 5.2 Tunnel through the moon 5.3 Gravitational eld above the center of a thin hoop 5.4 Gravitational force near a metal-cored planet surrounded by a gaseous cloud 5.5 Sphere with linearly increasing mass density 5.6 Jumping o Vesta 5.7 Gravitational force between two massive rods 5.8 Potential energy { Check your answer! 5.9 Ways of solving gravitational problems 5.10 Rod with linearly increasing mass density 5.11 Sphere with constant internal gravitational eld 5.12 Throwing a rock o the moon These problems are licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Un- ported License. Please share and/or modify. Back to Problem List 1 5 { GRAVITATION Last Updated: July 16, 2012 5.1 Total mass of a shell Given: Marino { Fall 2011 Consider a spherical shell that extends from r = R to r = 2R with a non-uniform density (r) = 0r. What is the total mass of the shell? Back to Problem List 2 5 { GRAVITATION Last Updated: July 16, 2012 5.2 Tunnel through the moon Given: Marino { Fall 2011 Imagine that NASA digs a straight tunnel through the center of the moon (see gure) to access the Moon’s 3He deposits. An astronaut places a rock in the tunnel at the surface of the moon, and releases it (from rest). Show that the rock obeys the force law for a mass connected to a spring. What is the spring constant? Find the oscillation period for this motion if you assume that Moon has a mass of 7.351022 kg and a radius of 1.74106 m. Assume the moon’s density is uniform throughout its volume, and ignore the moon’s rotation. Given: Pollock { Spring 2011 Imagine (in a parallel universe of unlimited budgets) that NASA digs a straight tunnel through the center of the moon (see gure). A robot place a rock in the tunnel at position r = r0 from the center of the moon, and releases it (from rest). Use Newton’s second law to write the equation of motion of the rock and solve for r(t). Explain in words the rock’s motion. Does the rock return to its initial position at any later time? If so, how long does it takes to return to it? (Give a formula, and a number.) Assume the moon’s density is uniform throughout its volume, and ignore the moon’s rotation. Given: Pollock { Spring 2012 Now lets consider our (real) planet Earth, with total mass M and radius R which we will approximate as a uniform mass density, (r) = 0. (a) Neglecting rotational and frictional e ects, show that a particle dropped into a hole drilled straight through the center of the earth all the way to the far side will oscillate between the two endpoints. (Hint: you will need to set up, and solve, an ODE for the motion) (b) Find the period of the oscillation of this motion. Get a number (in minutes) as a nal result, using data for the earth’s size and mass. (How does that compare to ying to Perth and back?!) Extra Credit: OK, even with unlimited budgets, digging a tunnel through the center of the earth is preposterous. But, suppose instead that the tunnel is a straight-line \chord” through the earth, say directly from New York to Los Angeles. Show that your nal answer for the time taken does not depend on the location of that chord! This is rather remarkable – look again at the time for a free-fall trip (no energy required, except perhaps to compensate for friction) How long would that trip take? Could this work?! Back to Problem List 3 5 { GRAVITATION Last Updated: July 16, 2012 5.3 Gravitational eld above the center of a thin hoop Given: Pollock { Spring 2011, Spring 2012 Consider a very (in nitesimally!) thin but massive loop, radius R (total mass M), centered around the origin, sitting in the x-y plane. Assume it has a uniform linear mass density  (which has units of kg/m) all around it. (So, it’s like a skinny donut that is mostly hole, centered around the z-axis) (a) What is  in terms of M and R? What is the direction of the gravitational eld generated by this mass distribution at a point in space a distance z above the center of the donut, i.e. at (0; 0; z) Explain your reasoning for the direction carefully, try not to simply \wave your hands.” (The answer is extremely intuitive, but can you justify that it is correct?) (b) Compute the gravitational eld, ~g, at the point (0; 0; z) by directly integrating Newton’s law of gravity, summing over all in nitesimal \chunks” of mass along the loop. (c) Compute the gravitational potential at the point (0; 0; z) by directly integrating ?Gdm=r, sum- ming over all in nitesimal \chunks” dm along the loop. Then, take the z-component of the gradient of this potential to check that you agree with your result from the previous part. (d) In the two separate limits z << R and z >> R, Taylor expand your g- eld (in the z-direction)out only to the rst non-zero term, and convince us that both limits make good physical sense. (e) Can you use Gauss’ law to gure out the gravitational potential at the point (0; 0; z)? (If so, do it and check your previous answers. If not, why not?) Extra credit: If you place a small mass a small distance z away from the center, use your Taylor limit for z << R above to write a simple ODE for the equation of motion. Solve it, and discuss the motion Back to Problem List 4 5 { GRAVITATION Last Updated: July 16, 2012 5.4 Gravitational force near a metal-cored planet surrounded by a gaseous cloud Given: Pollock { Spring 2011 Jupiter is composed of a dense spherical core (of liquid metallic hydrogen!) of radius Rc. It is sur- rounded by a spherical cloud of gaseous hydrogen of radius Rg, where Rg > Rc. Let’s assume that the core is of uniform density c and the gaseous cloud is also of uniform density g. What is the gravitational force on an object of mass m that is located at a radius r from the center of Jupiter? Note that you must consider the cases where the object is inside the core, within the gas layer, and outside of the planet. Back to Problem List 5 5 { GRAVITATION Last Updated: July 16, 2012 5.5 Sphere with linearly increasing mass density Given: Pollock { Spring 2011 A planet of mass M and radius R has a nonuniform density that varies with r, the distance from the center according to  = Ar for 0  r  R. (a) What is the constant A in terms of M and R? Does this density pro le strike you as physically plausible, or is just designed as a mathematical exercise? (Brie y, explain) (b) Determine the gravitational force on a satellite of mass m orbiting this planet. In words, please outline the method you plan to use for your solution. (Use the easiest method you can come up with!) In your calculation, you will need to argue that the magnitude of ~g(r; ; ) depends only on r. Be very explicit about this – how do you know that it doesn’t, in fact, depend on  or ? (c) Determine the gravitational force felt by a rock of mass m inside the planet, located at radius r < R. (If the method you use is di erent than in part b, explain why you switched. If not, just proceed!) Explicitly check your result for this part by considering the limits r ! 0 and r ! R. Back to Problem List 6 5 { GRAVITATION Last Updated: July 16, 2012 5.6 Jumping o Vesta Given: Pollock { Spring 2011 You are stranded on the surface of the asteroid Vesta. If the mass of the asteroid is M and its radius is R, how fast would you have to jump o its surface to be able to escape from its gravitational eld? (Your estimate should be based on parameters that characterize the asteroid, not parameters that describe your jumping ability.) Given your formula, look up the approximate mass and radius of the asteroid Vesta 3 and determine a numerical value of the escape velocity. Could you escape in this way? (Brie y, explain) If so, roughly how big in radius is the maximum the asteroid could be, for you to still escape this way? If not, estimate how much smaller an asteroid you would need, to escape from it in this way? Figure 1: Back to Problem List 7 5 { GRAVITATION Last Updated: July 16, 2012 5.7 Gravitational force between two massive rods Given: Pollock { Spring 2011 Consider two identical uniform rods of length L and mass m lying along the same line and having their closest points separated by a distance d as shown in the gure (a) Calculate the mutual force between these rods, both its direction and magnitude. (b) Now do several checks. First, make sure the units worked out (!) The, nd the magnitude of the force in the limit L ! 0. What do you expect? Brie y, discuss. Lastly, nd the magnitude of the force in the limit d ! 1 ? Again, is it what you expect? Brie y, discuss. Figure 2: Given: Pollock { Spring 2012 Determining the gravitational force between two rods: (a) Consider a thin, uniform rod of mass m and length L (and negligible other dimensions) lying on the x axis (from x=-L to 0), as shown in g 1a. Derive a formula for the gravitational eld \g" at any arbitrary point x to the right of the origin (but still on the x-axis!) due to this rod. (b) Now suppose a second rod of length L and mass m sits on the x axis as shown in g 1b, with the left edge a distance \d" away. Calculate the mutual gravitational force between these rods. (c) Let's do some checks! Show that the units work out in parts a and b. Find the magnitude of the force in part a, in the limit x >> L: What do you expect? Brie y, discuss! Finally, verify that your answer to part b gives what you expect in the limit d >> L. ( Hint: This is a bit harder! You need to consistently expand everything to second order, not just rst, because of some interesting cancellations) Fig 1a Fig 1b L m +x x=0 L x=0 x=d m Fig 1a Fig 1b L m +x x=0 L +x x=0 x=d L m m Back to Problem List 8 5 { GRAVITATION Last Updated: July 16, 2012 5.8 Potential energy { Check your answer! Given: Pollock { Spring 2011 On the last exam, we had a problem with a at ring, uniform mass per unit area of , inner radius of R, outer radius of 2R. A satellite (mass m) sat a distance z above the center of the ring. We asked for the gravitational potential energy, and the answer was U(z) = ?2Gm( p 4R2 + z2 ? p R2 + z2) (1) (a) If you are far from the disk (on the z axis), what do you expect for the formula for U(z)? (Don’t say \0″ – as usual, we want the functional form of U(z) as you move far away. Also, explicitly state what we mean by \far away”. (Please don’t compare something with units to something without units!) (b) Show explicitly that the formula above does indeed give precisely the functional dependence you expect. Back to Problem List 9 5 { GRAVITATION Last Updated: July 16, 2012 5.9 Ways of solving gravitational problems Given: Pollock { Spring 2011, Spring 2012 Infinite cylinder ρ=cr x z (a) Half-infinite line mass, uniform linear mass density, λ x (b) R z  P Figure 3: (a) An in nite cylinder of radius R centered on the z-axis, with non-uniform volume mass density  = cr, where r is the radius in cylindrical coordinates. (b) A half-in nite line of mass on the x-axis extending from x = 0 to x = +1, with uniform linear mass density . There are two general methods we use to solve gravitational problems (i.e. nd ~g given some distribution of mass). (a) Describe these two methods. We claim one of these methods is easiest to solve for ~g of mass distribution (a) above, and the other method is easiest to solve for ~g of the mass distribution (b) above. Which method goes with which mass distribution? Please justify your answer. (b) Find ~g of the mass distribution (a) above for any arbitrary point outside the cylinder. (c) Find the x component of the gravitational acceleration, gx, generated by the mass distribution labeled (b) above, at a point P a given distance z up the positive z-axis (as shown). Back to Problem List 10 5 { GRAVITATION Last Updated: July 16, 2012 5.10 Rod with linearly increasing mass density Given: Pollock { Spring 2012 Consider a very (in nitesimally!) thin but massive rod, length L (total mass M), centered around the origin, sitting along the x-axis. (So the left end is at (-L/2, 0,0) and the right end is at (+L/2,0,0) Assume the mass density  (which has units of kg/m)is not uniform, but instead varies linearly with distance from the origin, (x) = cjxj. (a) What is that constant \c” in terms of M and L? What is the direction of the gravitational eld generated by this mass distribution at a point in space a distance z above the center of the rod, i.e. at (0; 0; z) Explain your reasoning for the direction carefully, try not to simply \wave your hands.” (The answer is extremely intuitive, but can you justify that it is correct?) (b) Compute the gravitational eld, ~g, at the point (0; 0; z) by directly integrating Newton’s law of gravity, summing over all in nitesimal \chunks” of mass along the rod. (c) Compute the gravitational potential at the point (0; 0; z) by directly integrating ?Gdm=r, sum- ming over all in nitesimal \chunks” dm along the rod. Then, take the z-component of the gradient of this potential to check that you agree with your result from the previous part. (d) In the limit of large z what do you expect for the functional form for gravitational potential? (Hint: Don’t just say it goes to zero! It’s a rod of mass M, when you’re far away what does it look like? How does it go to zero?) What does \large z” mean here? Use the binomial (or Taylor) expansion to verify that your formula does indeed give exactly what you expect. (Hint: you cannot Taylor expand in something BIG, you have to Taylor expand in something small.) (e) Can you use Gauss’ law to gure out the gravitational potential at the point (0; 0; z)? (If so, do it and check your previous answers. If not, why not?) Back to Problem List 11 5 { GRAVITATION Last Updated: July 16, 2012 5.11 Sphere with constant internal gravitational eld Given: Pollock { Spring 2012 (a) Imagine a planet of total mass M and radius R which has a nonuniform mass density that varies just with r, the distance from the center. For this (admittedly very unusual!) planet, suppose the gravitational eld strength inside the planet turns out to be independent of the radial distance within the sphere. Find the function describing the mass density  = (r) of this planet. (Your nal answer should be written in terms of the given constants.) (b) Now, determine the gravitational force on a satellite of mass m orbiting this planet at distance r > R. (Use the easiest method you can come up with!) Explain your work in words as well as formulas. For instance, in your calculation, you will need to argue that the magnitude of ~g(r; ; ) depends only on r. Be explicit about this – how do you know that it doesn’t, in fact, depend on  or ? (c) As a nal check, explicitly show that your solutions inside and outside the planet (parts a and b) are consistent when r = R. Please also comment on whether this density pro le strikes you as physically plausible, or is it just designed as a mathematical exercise? Defend your reasoning. Back to Problem List 12 5 { GRAVITATION Last Updated: July 16, 2012 5.12 Throwing a rock o the moon Given: Pollock { Spring 2012 Assuming that asteroids have roughly the same mass density as the moon, make an estimate of the largest asteroid that an astronaut could be standing on, and still have a chance of throwing a small object (with their arms, no machinery!) so that it completely escapes the asteroid’s gravitational eld. (This minimum speed is called \escape velocity”) Is the size you computed typical for asteroids in our solar system? Back to Problem List 13

Chapter 8 Practice Problems (Practice – no credit) Due: 12:59pm on Friday, April 18, 2014 You will receive no credit for items you complete after the assignment is due. Grading Policy Circular Launch A ball is launched up a semicircular chute in such a way that at the top of the chute, just before it goes into free fall, the ball has a centripetal acceleration of magnitude 2 . Part A How far from the bottom of the chute does the ball land? Your answer for the distance the ball travels from the end of the chute should contain . You did not open hints for this part. ANSWER: g R Normal Force and Centripetal Force Ranking Task A roller-coaster track has six semicircular “dips” with different radii of curvature. The same roller-coaster cart rides through each dip at a different speed. Part A For the different values given for the radius of curvature and speed , rank the magnitude of the force of the roller-coaster track on the cart at the bottom of each dip. Rank from largest to smallest. To rank items as equivalent, overlap them. You did not open hints for this part. ANSWER: D = R v Two Cars on a Curving Road Part A A small car of mass and a large car of mass drive along a highway. They approach a curve of radius . Both cars maintain the same acceleration as they travel around the curve. How does the speed of the small car compare to the speed of the large car as they round the curve? You did not open hints for this part. m 4m R a vS vL ANSWER: Part B Now assume that two identical cars of mass drive along a highway. One car approaches a curve of radius at speed . The second car approaches a curve of radius at a speed of . How does the magnitude of the net force exerted on the first car compare to the magnitude of the net force exerted on the second car? You did not open hints for this part. ANSWER: ± A Ride on the Ferris Wheel A woman rides on a Ferris wheel of radius 16 that maintains the same speed throughout its motion. To better understand physics, she takes along a digital bathroom scale (with memory) and sits on it. When she gets off the ride, she uploads the scale readings to a computer and creates a graph of scale reading versus time. Note that the graph has a minimum value of 510 and a maximum value of 666 . vS = 1 4 vL vS = 1 2 vL vS = vL vS = 2vL vS = 4vL m 2R v 6R 3v F1 F2 F1 = 1 3 F2 F1 = 3 4 F2 F1 = F2 F1 = 3F2 F1 = 27F2 m N N Part A What is the woman’s mass? Express your answer in kilograms. You did not open hints for this part. ANSWER: ± Mass on Turntable A small metal cylinder rests on a circular turntable that is rotating at a constant speed as illustrated in the diagram . The small metal cylinder has a mass of 0.20 , the coefficient of static friction between the cylinder and the turntable is 0.080, and the cylinder is located 0.15 from the center of the turntable. Take the magnitude of the acceleration due to gravity to be 9.81 . m = kg kg m m/s2 Part A What is the maximum speed that the cylinder can move along its circular path without slipping off the turntable? Express your answer numerically in meters per second to two significant figures. You did not open hints for this part. ANSWER: Score Summary: Your score on this assignment is 0%. You received 0 out of a possible total of 0 points. vmax vmax = m/s

Chapter 8 Practice Problems (Practice – no credit) Due: 12:59pm on Friday, April 18, 2014 You will receive no credit for items you complete after the assignment is due. Grading Policy Circular Launch A ball is launched up a semicircular chute in such a way that at the top of the chute, just before it goes into free fall, the ball has a centripetal acceleration of magnitude 2 . Part A How far from the bottom of the chute does the ball land? Your answer for the distance the ball travels from the end of the chute should contain . You did not open hints for this part. ANSWER: g R Normal Force and Centripetal Force Ranking Task A roller-coaster track has six semicircular “dips” with different radii of curvature. The same roller-coaster cart rides through each dip at a different speed. Part A For the different values given for the radius of curvature and speed , rank the magnitude of the force of the roller-coaster track on the cart at the bottom of each dip. Rank from largest to smallest. To rank items as equivalent, overlap them. You did not open hints for this part. ANSWER: D = R v Two Cars on a Curving Road Part A A small car of mass and a large car of mass drive along a highway. They approach a curve of radius . Both cars maintain the same acceleration as they travel around the curve. How does the speed of the small car compare to the speed of the large car as they round the curve? You did not open hints for this part. m 4m R a vS vL ANSWER: Part B Now assume that two identical cars of mass drive along a highway. One car approaches a curve of radius at speed . The second car approaches a curve of radius at a speed of . How does the magnitude of the net force exerted on the first car compare to the magnitude of the net force exerted on the second car? You did not open hints for this part. ANSWER: ± A Ride on the Ferris Wheel A woman rides on a Ferris wheel of radius 16 that maintains the same speed throughout its motion. To better understand physics, she takes along a digital bathroom scale (with memory) and sits on it. When she gets off the ride, she uploads the scale readings to a computer and creates a graph of scale reading versus time. Note that the graph has a minimum value of 510 and a maximum value of 666 . vS = 1 4 vL vS = 1 2 vL vS = vL vS = 2vL vS = 4vL m 2R v 6R 3v F1 F2 F1 = 1 3 F2 F1 = 3 4 F2 F1 = F2 F1 = 3F2 F1 = 27F2 m N N Part A What is the woman’s mass? Express your answer in kilograms. You did not open hints for this part. ANSWER: ± Mass on Turntable A small metal cylinder rests on a circular turntable that is rotating at a constant speed as illustrated in the diagram . The small metal cylinder has a mass of 0.20 , the coefficient of static friction between the cylinder and the turntable is 0.080, and the cylinder is located 0.15 from the center of the turntable. Take the magnitude of the acceleration due to gravity to be 9.81 . m = kg kg m m/s2 Part A What is the maximum speed that the cylinder can move along its circular path without slipping off the turntable? Express your answer numerically in meters per second to two significant figures. You did not open hints for this part. ANSWER: Score Summary: Your score on this assignment is 0%. You received 0 out of a possible total of 0 points. vmax vmax = m/s

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ECON 101 FALL 2015 EXAM 1 NAME:______________________________ 1. Suppose the price elasticity of demand for cheeseburgers equals 1.37. This means the overall demand for cheeseburgers is: A) price elastic. B) price inelastic. C) price unit-elastic. D) perfectly price inelastic. 2. The price elasticity of demand for skiing lessons in New Hampshire is less than 1.00. This means that the demand is ______ in New Hampshire. A) price elastic B) price inelastic C) price unit-elastic D) perfectly price elastic 3. If the demand for textbooks is price inelastic, which of the following would explain this? A) Many alternative textbooks can be used as substitutes. B) Students have a lot of time to adjust to price changes. C) Textbook purchases consume a large portion of most students’ income. D) The good is a necessity. 4. A major state university in the South recently raised tuition by 12%. An economics professor at this university asked his students, “Due to the increase in tuition, how many of you will transfer to another university?” One student out of about 300 said that he or she would transfer. Based on this information, the price elasticity of demand for education at this university is: (Hint: one out of 300 is how much of a percentage change? Which percentage change is greater – tuition or transfer? Apply the basic formula for elasticity that I put on the board a few times.) A) one. B) highly elastic. C) highly inelastic. D) zero. 5. Suppose the price elasticity of demand for fishing lures equals 1 in South Carolina and 0.63 in Alabama. To increase revenue, fishing lure manufacturers should: (Hint: If the demand for a product is inelastic, the price can go up and you’ll still buy it, since there are no or few substitutes. If the demand for a product is elastic, the price can go up and you’ll probably walk away from it, since substitutes are available. How might this info impact the pricing strategies of firms?) A) lower prices in each state. B) raise prices in each state. C) lower prices in South Carolina and raise prices in Alabama. D) leave prices unchanged in South Carolina and raise prices in Alabama. Read your syllabus and answer questions 6 through 10: 6. T or F: Disruptive classroom behavior includes the following: chatting with fellow students, use of electronic devices such as laptops, tablets, notebooks, and cell phones, reading or studying during class, sleeping, arriving late, departing early, studying for another class, or in any other way disturbing the class. 7. T or F: It’s OK to use my computer in class or play with my phone. There is no penalty attached to these activities and Keiser doesn’t really mind. 8. T or F: It’s OK to show up late for class and disrupt one of Keiser’s swashbuckling lectures. 9. T or F: Attendance is highly optional since it doesn’t impact my final course grade. 10. T or F: I should blow off the career plan/business plan assignment in this course because it’s unimportant to my future and not worth many points. 11. Jacquelyn is a student at a major state university. Which of the following is not an example of an explicit, or direct, cost of her attending college? A) Tuition B) Textbooks C) the salary that she could have earned working full time D) computer lab fees 12. The two principles of tax fairness are: A) the minimize distortions principle and the maximize revenue principle. B) the benefits principle and the ability-to-pay principle. C) the proportional tax principle and the ability-to-pay principle. D) the equity principle and the efficiency principle. 13. The benefits principles says: A) the amount of tax paid depends on the measure of value. B) those who benefit from public spending should bear the burden of the tax that pays for that spending. C) those with greater ability to pay should pay more tax. D) those who benefit from the tax should pay the same percentage of the tax base as those who do not benefit. 14. A tax that rises less than in proportion to income is described as: (Hint: This would have more of a negative impact on lower income earners vs. higher income earners.) A) progressive. B) proportional. C) regressive. D) structural. 15. The U.S. income tax is _______, while the payroll tax is _______. (Hint: Think income tax vs. Social Security tax.) A) progressive; progressive C) regressive; progressive B) progressive; regressive D) regressive; regressive 16. Who is currently leading in the polls to receive the Republican nomination as that party’s presidential candidate? A) Qasem Soleimani B) Abu Bakr al-Baghdadi C) Osama bin Laden D) Donald J. Trump 17. The single most important thing I’ve learned in class this term is: A) stay in frickin’ school B) stay in school and make a plan for life and my career C) the use of cheese for skyscraper construction D) both A and B above 18. Market equilibrium occurs when: A) there is no incentive for prices to change in the market. B) quantity demanded equals quantity supplied. C) the market clears. D) all of the above occur. 19. Excess supply occurs when: (Hint: Draw a supply and demand graph! Think about price ceilings and floors and the graphs of these we discussed in class.) A) the price is above the equilibrium price. B) the quantity demanded exceeds the quantity supplied. C) the price is below the equilibrium price. D) both b and c occur. 20. The single most important thing I’ve learned in class this term is: a. stay in school and look into either a study abroad or internship experience b. stay in school and make a plan for life and my career c. the untimely demise of Cecil the lion in Zimbabwe d. both a. and b. above 21. According to the textbook definition, mainstream microeconomics generally focuses on a. how individual decision-making units, like households and firms, make economic decisions. b. the performance of the national economy and policies to improve this performance. c. the relationship between economic and political institutions. d. the general level of prices in the national economy. 22. Which of the following is the best summary of the three basic economic questions? a. Who? Why? and When? b. What? How? and Who? c. When? Where? and Why? d. What? Where? and Who? 23. Which of the following is not one of the basic economic resources? a. land b. labor c. capital d. cheese e. entrepreneurship 24. The largest country in the Arabian Peninsula and home to the cities of Riyadh, Jeddah, Mecca, and Medina is: a. The Kingdom of Saudi Arabia b. California c. Spain d. Kentucky 25. T or F: The law of demand explains the upward slope of the supply curve. 26. In economics, a “marginal” value refers to: a. the value associated with an important or marginal activity. b. a value entered as an explanatory item in the margin of a balance sheet or other accounts. c. the value associated with one more unit of an activity. d. a value that is most appropriately identified in a footnote. 27. A government mandated price that is below the market equilibrium price is sometimes called. . . (Hint: Draw a graph again and think about what the government is trying to accomplish.) a. a price ceiling. b. a price floor. c. a market clearing price. d. a reservation price. 28. T or F: Entering the US job market without any education or training is crazy and should be avoided. Stay in frickin’ school, baby! 29. The law of demand states that, other things equal: a. as the price increases, the quantity demanded will increase. b. as the price decreases, the demand curve will shift to the right. c. as the price increases, the quantity demanded will decrease. d. none of the above. 30. The law of supply says: a. other things equal, the quantity supplied of a good is inversely related to the price of the good. b. other things equal, the supply of a good creates its own demand. c. other things equal, the quantity supplied of a good is positively related to the price of the good. d. none of the above. 31. A perfectly inelastic demand curve is: a. horizontal. b. downward sloping. c. upward sloping. d. vertical. 32. A trade-off involves weighing costs and benefits. a. true b. false 33. A perfectly elastic demand curve is: a. horizontal. b. downward sloping. c. upward sloping. d. vertical. 34. The second most important thing I’ve learned in class this term is: a. despair is not an option b. Donald J. Trump’s hair is real c. the use of cheese for skyscraper construction d. none of the above 35. T or F: Virtually any news item has important economic dimensions and consequences. 36. T or F: When studying economics, always think in terms of historical context. 37. This popular Asian country is populated by 1.3 billion people, has the world’s second largest economy, and uses a language that’s been in continuous use for nearly 5,000 years: a. Kentucky b. California c. Spain d. China 38. T or F: The top priority in my life right now should be my education and an internship experience. Without these, the job market is going to kick my butt! 39. Which of the following is a key side effect generated by the use of price ceilings? a. black markets b. products with too high of quality c. an excess supply of a good d. too many resources artificially channeled into the production of a good 40. Which of the following is NOT one of the four basic principles for understanding individual choice? a. Resources are scarce. b. The real cost of something is the money that you must pay to get it. c. “How much?” is a decision at the margin. d. People usually take advantage of opportunities to make themselves better off. 41. A hot mixture of pan drippings, flour, and water is commonly known as: a. interest rates and expected future real GDP. b. interest rates and current real GDP. c. inflation and expected future real GDP. d. gravy. 42. The example we used in class when discussing the inefficiency of quantity quotas was: a. Uber b. General Electric c. AT&T d. the KSU marching band 43. The term we learned in class signifying a key method of non-price competition is: a. excess supply chain management b. arbitrage c. swashbuckling d. product differentiation 44. When discussing market failure and the role of regulation in class, which company/product did we use as an example? a. Pabst Blue Ribbon b. JetBlue c. Blue Bell d. Blue Apron 45. Governments may place relatively high sales taxes on goods such as alcohol and tobacco because: a. such taxes are a significant source of revenue b. such goods exhibit inelastic demand c. such taxes may discourage use of these products d. all of the above 46. When discussing the cost of higher education in class, which country did we cite as an example of one that offers free college for qualifying students? a. USSR b. Rhodesia c. Czechoslovakia d. Germany 47. Which of the following is not an example of market failure we discussed in class? a. externalities b. public goods c. fungible goods d. common pool resources e. equity 48. T or F: As we discussed in class, the real reason why the US has lost jobs to China is the “most favored nation” (MFN) trading status granted to China by the US back in the 1980s. 49. The dude we talked about in class who coined the expression “invisible hand” and promoted self-interest and competition in his famous book “The Wealth of Nations” is: a. Abu Bakr al-Baghdadi b. Ali Khamenei c. Donald J. Trump d. Adam Smith 50. When studying for your final exams and attempting to allocate your limited time among several subjects in order to maximize your course grades (recall, we talked about this example during the first week of class), you’re almost unconsciously engaging in a form of: a. fraud b. miscellaneous serendipity b. mitosis d. marginal analysis

ECON 101 FALL 2015 EXAM 1 NAME:______________________________ 1. Suppose the price elasticity of demand for cheeseburgers equals 1.37. This means the overall demand for cheeseburgers is: A) price elastic. B) price inelastic. C) price unit-elastic. D) perfectly price inelastic. 2. The price elasticity of demand for skiing lessons in New Hampshire is less than 1.00. This means that the demand is ______ in New Hampshire. A) price elastic B) price inelastic C) price unit-elastic D) perfectly price elastic 3. If the demand for textbooks is price inelastic, which of the following would explain this? A) Many alternative textbooks can be used as substitutes. B) Students have a lot of time to adjust to price changes. C) Textbook purchases consume a large portion of most students’ income. D) The good is a necessity. 4. A major state university in the South recently raised tuition by 12%. An economics professor at this university asked his students, “Due to the increase in tuition, how many of you will transfer to another university?” One student out of about 300 said that he or she would transfer. Based on this information, the price elasticity of demand for education at this university is: (Hint: one out of 300 is how much of a percentage change? Which percentage change is greater – tuition or transfer? Apply the basic formula for elasticity that I put on the board a few times.) A) one. B) highly elastic. C) highly inelastic. D) zero. 5. Suppose the price elasticity of demand for fishing lures equals 1 in South Carolina and 0.63 in Alabama. To increase revenue, fishing lure manufacturers should: (Hint: If the demand for a product is inelastic, the price can go up and you’ll still buy it, since there are no or few substitutes. If the demand for a product is elastic, the price can go up and you’ll probably walk away from it, since substitutes are available. How might this info impact the pricing strategies of firms?) A) lower prices in each state. B) raise prices in each state. C) lower prices in South Carolina and raise prices in Alabama. D) leave prices unchanged in South Carolina and raise prices in Alabama. Read your syllabus and answer questions 6 through 10: 6. T or F: Disruptive classroom behavior includes the following: chatting with fellow students, use of electronic devices such as laptops, tablets, notebooks, and cell phones, reading or studying during class, sleeping, arriving late, departing early, studying for another class, or in any other way disturbing the class. 7. T or F: It’s OK to use my computer in class or play with my phone. There is no penalty attached to these activities and Keiser doesn’t really mind. 8. T or F: It’s OK to show up late for class and disrupt one of Keiser’s swashbuckling lectures. 9. T or F: Attendance is highly optional since it doesn’t impact my final course grade. 10. T or F: I should blow off the career plan/business plan assignment in this course because it’s unimportant to my future and not worth many points. 11. Jacquelyn is a student at a major state university. Which of the following is not an example of an explicit, or direct, cost of her attending college? A) Tuition B) Textbooks C) the salary that she could have earned working full time D) computer lab fees 12. The two principles of tax fairness are: A) the minimize distortions principle and the maximize revenue principle. B) the benefits principle and the ability-to-pay principle. C) the proportional tax principle and the ability-to-pay principle. D) the equity principle and the efficiency principle. 13. The benefits principles says: A) the amount of tax paid depends on the measure of value. B) those who benefit from public spending should bear the burden of the tax that pays for that spending. C) those with greater ability to pay should pay more tax. D) those who benefit from the tax should pay the same percentage of the tax base as those who do not benefit. 14. A tax that rises less than in proportion to income is described as: (Hint: This would have more of a negative impact on lower income earners vs. higher income earners.) A) progressive. B) proportional. C) regressive. D) structural. 15. The U.S. income tax is _______, while the payroll tax is _______. (Hint: Think income tax vs. Social Security tax.) A) progressive; progressive C) regressive; progressive B) progressive; regressive D) regressive; regressive 16. Who is currently leading in the polls to receive the Republican nomination as that party’s presidential candidate? A) Qasem Soleimani B) Abu Bakr al-Baghdadi C) Osama bin Laden D) Donald J. Trump 17. The single most important thing I’ve learned in class this term is: A) stay in frickin’ school B) stay in school and make a plan for life and my career C) the use of cheese for skyscraper construction D) both A and B above 18. Market equilibrium occurs when: A) there is no incentive for prices to change in the market. B) quantity demanded equals quantity supplied. C) the market clears. D) all of the above occur. 19. Excess supply occurs when: (Hint: Draw a supply and demand graph! Think about price ceilings and floors and the graphs of these we discussed in class.) A) the price is above the equilibrium price. B) the quantity demanded exceeds the quantity supplied. C) the price is below the equilibrium price. D) both b and c occur. 20. The single most important thing I’ve learned in class this term is: a. stay in school and look into either a study abroad or internship experience b. stay in school and make a plan for life and my career c. the untimely demise of Cecil the lion in Zimbabwe d. both a. and b. above 21. According to the textbook definition, mainstream microeconomics generally focuses on a. how individual decision-making units, like households and firms, make economic decisions. b. the performance of the national economy and policies to improve this performance. c. the relationship between economic and political institutions. d. the general level of prices in the national economy. 22. Which of the following is the best summary of the three basic economic questions? a. Who? Why? and When? b. What? How? and Who? c. When? Where? and Why? d. What? Where? and Who? 23. Which of the following is not one of the basic economic resources? a. land b. labor c. capital d. cheese e. entrepreneurship 24. The largest country in the Arabian Peninsula and home to the cities of Riyadh, Jeddah, Mecca, and Medina is: a. The Kingdom of Saudi Arabia b. California c. Spain d. Kentucky 25. T or F: The law of demand explains the upward slope of the supply curve. 26. In economics, a “marginal” value refers to: a. the value associated with an important or marginal activity. b. a value entered as an explanatory item in the margin of a balance sheet or other accounts. c. the value associated with one more unit of an activity. d. a value that is most appropriately identified in a footnote. 27. A government mandated price that is below the market equilibrium price is sometimes called. . . (Hint: Draw a graph again and think about what the government is trying to accomplish.) a. a price ceiling. b. a price floor. c. a market clearing price. d. a reservation price. 28. T or F: Entering the US job market without any education or training is crazy and should be avoided. Stay in frickin’ school, baby! 29. The law of demand states that, other things equal: a. as the price increases, the quantity demanded will increase. b. as the price decreases, the demand curve will shift to the right. c. as the price increases, the quantity demanded will decrease. d. none of the above. 30. The law of supply says: a. other things equal, the quantity supplied of a good is inversely related to the price of the good. b. other things equal, the supply of a good creates its own demand. c. other things equal, the quantity supplied of a good is positively related to the price of the good. d. none of the above. 31. A perfectly inelastic demand curve is: a. horizontal. b. downward sloping. c. upward sloping. d. vertical. 32. A trade-off involves weighing costs and benefits. a. true b. false 33. A perfectly elastic demand curve is: a. horizontal. b. downward sloping. c. upward sloping. d. vertical. 34. The second most important thing I’ve learned in class this term is: a. despair is not an option b. Donald J. Trump’s hair is real c. the use of cheese for skyscraper construction d. none of the above 35. T or F: Virtually any news item has important economic dimensions and consequences. 36. T or F: When studying economics, always think in terms of historical context. 37. This popular Asian country is populated by 1.3 billion people, has the world’s second largest economy, and uses a language that’s been in continuous use for nearly 5,000 years: a. Kentucky b. California c. Spain d. China 38. T or F: The top priority in my life right now should be my education and an internship experience. Without these, the job market is going to kick my butt! 39. Which of the following is a key side effect generated by the use of price ceilings? a. black markets b. products with too high of quality c. an excess supply of a good d. too many resources artificially channeled into the production of a good 40. Which of the following is NOT one of the four basic principles for understanding individual choice? a. Resources are scarce. b. The real cost of something is the money that you must pay to get it. c. “How much?” is a decision at the margin. d. People usually take advantage of opportunities to make themselves better off. 41. A hot mixture of pan drippings, flour, and water is commonly known as: a. interest rates and expected future real GDP. b. interest rates and current real GDP. c. inflation and expected future real GDP. d. gravy. 42. The example we used in class when discussing the inefficiency of quantity quotas was: a. Uber b. General Electric c. AT&T d. the KSU marching band 43. The term we learned in class signifying a key method of non-price competition is: a. excess supply chain management b. arbitrage c. swashbuckling d. product differentiation 44. When discussing market failure and the role of regulation in class, which company/product did we use as an example? a. Pabst Blue Ribbon b. JetBlue c. Blue Bell d. Blue Apron 45. Governments may place relatively high sales taxes on goods such as alcohol and tobacco because: a. such taxes are a significant source of revenue b. such goods exhibit inelastic demand c. such taxes may discourage use of these products d. all of the above 46. When discussing the cost of higher education in class, which country did we cite as an example of one that offers free college for qualifying students? a. USSR b. Rhodesia c. Czechoslovakia d. Germany 47. Which of the following is not an example of market failure we discussed in class? a. externalities b. public goods c. fungible goods d. common pool resources e. equity 48. T or F: As we discussed in class, the real reason why the US has lost jobs to China is the “most favored nation” (MFN) trading status granted to China by the US back in the 1980s. 49. The dude we talked about in class who coined the expression “invisible hand” and promoted self-interest and competition in his famous book “The Wealth of Nations” is: a. Abu Bakr al-Baghdadi b. Ali Khamenei c. Donald J. Trump d. Adam Smith 50. When studying for your final exams and attempting to allocate your limited time among several subjects in order to maximize your course grades (recall, we talked about this example during the first week of class), you’re almost unconsciously engaging in a form of: a. fraud b. miscellaneous serendipity b. mitosis d. marginal analysis

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Math 285 Quiz One Name: ________________ 1. The product of these two matrices 5 2 2 −1  4 −2 1 3  is (Please show your work for full credit.) 2. For what value of a is this determinant equal to 0? 0 5 2 0 1 −8 −4 2 (please justify your answer.) 3. What is the product of these matrices? 3 2 6 −2 1 0 4 1 0   2346  (Please justify your answer.) 4. What is the largest possible number of pivots a 7 × 5 matrix can have? (Please justify your answer.) Homework 1 5. Find the standard matrix of the linear transformation : →  which rotates a point about the origin through an angle of   radians (counterclockwise). True or False (Simply enter T or F, no need to justify the answer) If matrices  and  are row equivalent, they have the same reduced echelon form. In general,  +  ≠  +  (assume  and  are  x  matrices). If a matrix  is symmetric, then so is  + “#. A matrix  must be a square matrix to be invertible. If $%&’( ≠ 0, then columns of  are linearly independent. If an  x  matrix  is equivalent to “#, then )* is also equivalent to “#. If an + x  matrix  has a pivot position in every row, then the equation , = . has a unique solution for each . in /0. If  = “, then  is invertible.

Math 285 Quiz One Name: ________________ 1. The product of these two matrices 5 2 2 −1  4 −2 1 3  is (Please show your work for full credit.) 2. For what value of a is this determinant equal to 0? 0 5 2 0 1 −8 −4 2 (please justify your answer.) 3. What is the product of these matrices? 3 2 6 −2 1 0 4 1 0   2346  (Please justify your answer.) 4. What is the largest possible number of pivots a 7 × 5 matrix can have? (Please justify your answer.) Homework 1 5. Find the standard matrix of the linear transformation : →  which rotates a point about the origin through an angle of   radians (counterclockwise). True or False (Simply enter T or F, no need to justify the answer) If matrices  and  are row equivalent, they have the same reduced echelon form. In general,  +  ≠  +  (assume  and  are  x  matrices). If a matrix  is symmetric, then so is  + “#. A matrix  must be a square matrix to be invertible. If $%&’( ≠ 0, then columns of  are linearly independent. If an  x  matrix  is equivalent to “#, then )* is also equivalent to “#. If an + x  matrix  has a pivot position in every row, then the equation , = . has a unique solution for each . in /0. If  = “, then  is invertible.

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Chapter 9 Practice Problems (Practice – no credit) Due: 11:59pm on Friday, April 18, 2014 You will receive no credit for items you complete after the assignment is due. Grading Policy Momentum and Internal Forces Learning Goal: To understand the concept of total momentum for a system of objects and the effect of the internal forces on the total momentum. We begin by introducing the following terms: System: Any collection of objects, either pointlike or extended. In many momentum-related problems, you have a certain freedom in choosing the objects to be considered as your system. Making a wise choice is often a crucial step in solving the problem. Internal force: Any force interaction between two objects belonging to the chosen system. Let us stress that both interacting objects must belong to the system. External force: Any force interaction between objects at least one of which does not belong to the chosen system; in other words, at least one of the objects is external to the system. Closed system: a system that is not subject to any external forces. Total momentum: The vector sum of the individual momenta of all objects constituting the system. In this problem, you will analyze a system composed of two blocks, 1 and 2, of respective masses and . To simplify the analysis, we will make several assumptions: The blocks can move in only one dimension, namely, 1. along the x axis. 2. The masses of the blocks remain constant. 3. The system is closed. At time , the x components of the velocity and the acceleration of block 1 are denoted by and . Similarly, the x components of the velocity and acceleration of block 2 are denoted by and . In this problem, you will show that the total momentum of the system is not changed by the presence of internal forces. m1 m2 t v1(t) a1 (t) v2 (t) a2 (t) Part A Find , the x component of the total momentum of the system at time . Express your answer in terms of , , , and . ANSWER: Part B Find the time derivative of the x component of the system’s total momentum. Express your answer in terms of , , , and . You did not open hints for this part. ANSWER: Why did we bother with all this math? The expression for the derivative of momentum that we just obtained will be useful in reaching our desired conclusion, if only for this very special case. Part C The quantity (mass times acceleration) is dimensionally equivalent to which of the following? ANSWER: p(t) t m1 m2 v1 (t) v2 (t) p(t) = dp(t)/dt a1 (t) a2 (t) m1 m2 dp(t)/dt = ma Part D Acceleration is due to which of the following physical quantities? ANSWER: Part E Since we have assumed that the system composed of blocks 1 and 2 is closed, what could be the reason for the acceleration of block 1? You did not open hints for this part. ANSWER: momentum energy force acceleration inertia velocity speed energy momentum force Part F This question will be shown after you complete previous question(s). Part G Let us denote the x component of the force exerted by block 1 on block 2 by , and the x component of the force exerted by block 2 on block 1 by . Which of the following pairs equalities is a direct consequence of Newton’s second law? ANSWER: Part H Let us recall that we have denoted the force exerted by block 1 on block 2 by , and the force exerted by block 2 on block 1 by . If we suppose that is greater than , which of the following statements about forces is true? You did not open hints for this part. the large mass of block 1 air resistance Earth’s gravitational attraction a force exerted by block 2 on block 1 a force exerted by block 1 on block 2 F12 F21 and and and and F12 = m2a2 F21 = m1a1 F12 = m1a1 F21 = m2a2 F12 = m1a2 F21 = m2a1 F12 = m2a1 F21 = m1a2 F12 F21 m1 m2 ANSWER: Part I Now recall the expression for the time derivative of the x component of the system’s total momentum: . Considering the information that you now have, choose the best alternative for an equivalent expression to . You did not open hints for this part. ANSWER: Impulse and Momentum Ranking Task Six automobiles are initially traveling at the indicated velocities. The automobiles have different masses and velocities. The drivers step on the brakes and all automobiles are brought to rest. Part A Rank these automobiles based on the magnitude of their momentum before the brakes are applied, from largest to smallest. Rank from largest to smallest. To rank items as equivalent, overlap them. If the ranking cannot be determined, check the box below. ANSWER: Both forces have equal magnitudes. |F12 | > |F21| |F21 | > |F12| dpx(t)/dt = Fx dpx(t)/dt 0 nonzero constant kt kt2 Part B Rank these automobiles based on the magnitude of the impulse needed to stop them, from largest to smallest. Rank from largest to smallest. To rank items as equivalent, overlap them. If the ranking cannot be determined, check the box below. You did not open hints for this part. ANSWER: Part C Rank the automobiles based on the magnitude of the force needed to stop them, from largest to smallest. Rank from largest to smallest. To rank items as equivalent, overlap them. If the ranking cannot be determined, check the box below. You did not open hints for this part. ANSWER: A Game of Frictionless Catch Chuck and Jackie stand on separate carts, both of which can slide without friction. The combined mass of Chuck and his cart, , is identical to the combined mass of Jackie and her cart. Initially, Chuck and Jackie and their carts are at rest. Chuck then picks up a ball of mass and throws it to Jackie, who catches it. Assume that the ball travels in a straight line parallel to the ground (ignore the effect of gravity). After Chuck throws the ball, his speed relative to the ground is . The speed of the thrown ball relative to the ground is . Jackie catches the ball when it reaches her, and she and her cart begin to move. Jackie’s speed relative to the ground after she catches the ball is . When answering the questions in this problem, keep the following in mind: The original mass of Chuck and his cart does not include the 1. mass of the ball. 2. The speed of an object is the magnitude of its velocity. An object’s speed will always be a nonnegative quantity. mcart mball vc vb vj mcart Part A Find the relative speed between Chuck and the ball after Chuck has thrown the ball. Express the speed in terms of and . You did not open hints for this part. ANSWER: Part B What is the speed of the ball (relative to the ground) while it is in the air? Express your answer in terms of , , and . You did not open hints for this part. ANSWER: Part C What is Chuck’s speed (relative to the ground) after he throws the ball? Express your answer in terms of , , and . u vc vb u = vb mball mcart u vb = vc mball mcart u You did not open hints for this part. ANSWER: Part D Find Jackie’s speed (relative to the ground) after she catches the ball, in terms of . Express in terms of , , and . You did not open hints for this part. ANSWER: Part E Find Jackie’s speed (relative to the ground) after she catches the ball, in terms of . Express in terms of , , and . You did not open hints for this part. ANSWER: vc = vj vb vj mball mcart vb vj = vj u vj mball mcart u Momentum in an Explosion A giant “egg” explodes as part of a fireworks display. The egg is at rest before the explosion, and after the explosion, it breaks into two pieces, with the masses indicated in the diagram, traveling in opposite directions. Part A What is the momentum of piece A before the explosion? Express your answer numerically in kilogram meters per second. You did not open hints for this part. ANSWER: vj = pA,i Part B During the explosion, is the force of piece A on piece B greater than, less than, or equal to the force of piece B on piece A? You did not open hints for this part. ANSWER: Part C The momentum of piece B is measured to be 500 after the explosion. Find the momentum of piece A after the explosion. Enter your answer numerically in kilogram meters per second. You did not open hints for this part. ANSWER: pA,i = kg  m/s greater than less than equal to cannot be determined kg  m/s pA,f pA,f = kg  m/s ± PSS 9.1 Conservation of Momentum Learning Goal: To practice Problem-Solving Strategy 9.1 for conservation of momentum problems. An 80- quarterback jumps straight up in the air right before throwing a 0.43- football horizontally at 15 . How fast will he be moving backward just after releasing the ball? PROBLEM-SOLVING STRATEGY 9.1 Conservation of momentum MODEL: Clearly define the system. If possible, choose a system that is isolated ( ) or within which the interactions are sufficiently short and intense that you can ignore external forces for the duration of the interaction (the impulse approximation). Momentum is conserved. If it is not possible to choose an isolated system, try to divide the problem into parts such that momentum is conserved during one segment of the motion. Other segments of the motion can be analyzed using Newton’s laws or, as you will learn later, conservation of energy. VISUALIZE: Draw a before-and-after pictorial representation. Define symbols that will be used in the problem, list known values, and identify what you are trying to find. SOLVE: The mathematical representation is based on the law of conservation of momentum: . In component form, this is ASSESS: Check that your result has the correct units, is reasonable, and answers the question. Model The interaction at study in this problem is the action of throwing the ball, performed by the quarterback while being off the ground. To apply conservation of momentum to this interaction, you will need to clearly define a system that is isolated or within which the impulse approximation can be applied. Part A Sort the following objects as part of the system or not. Drag the appropriate objects to their respective bins. ANSWER: kg kg m/s F = net 0 P = f P  i (pfx + ( + ( += ( + ( + ( + )1 pfx)2 pfx)3 pix)1 pix)2 pix)3 (pfy + ( + ( += ( + ( + ( + )1 pfy)2 pfy)3 piy)1 piy)2 piy)3 Part B This question will be shown after you complete previous question(s). Visualize Solve Part C This question will be shown after you complete previous question(s). Assess Part D This question will be shown after you complete previous question(s). Conservation of Momentum in Inelastic Collisions Learning Goal: To understand the vector nature of momentum in the case in which two objects collide and stick together. In this problem we will consider a collision of two moving objects such that after the collision, the objects stick together and travel off as a single unit. The collision is therefore completely inelastic. You have probably learned that “momentum is conserved” in an inelastic collision. But how does this fact help you to solve collision problems? The following questions should help you to clarify the meaning and implications of the statement “momentum is conserved.” Part A What physical quantities are conserved in this collision? ANSWER: Part B Two cars of equal mass collide inelastically and stick together after the collision. Before the collision, their speeds are and . What is the speed of the two-car system after the collision? the magnitude of the momentum only the net momentum (considered as a vector) only the momentum of each object considered individually v1 v2 You did not open hints for this part. ANSWER: Part C Two cars collide inelastically and stick together after the collision. Before the collision, the magnitudes of their momenta are and . After the collision, what is the magnitude of their combined momentum? You did not open hints for this part. ANSWER: The answer depends on the directions in which the cars were moving before the collision. v1 + v2 v1 − v2 v2 − v1 v1v2 −−−− ” v1+v2 2 v1 + 2 v2 2 −−−−−−−  p1 p2 Part D Two cars collide inelastically and stick together after the collision. Before the collision, their momenta are and . After the collision, their combined momentum is . Of what can one be certain? You did not open hints for this part. ANSWER: Part E Two cars collide inelastically and stick together after the collision. Before the collision, the magnitudes of their momenta are and . After the collision, the magnitude of their combined momentum is . Of what can one be certain? The answer depends on the directions in which the cars were moving before the collision. p1 + p2 p1 − p2 p2 − p1 p1p2 −−−− ” p1+p2 2 p1 + 2 p2 2 −−−−−−−  p 1 p 2 p p = p1 + # p2 # p = p1 − # p2 # p = p2 − # p1 # p1 p2 p You did not open hints for this part. ANSWER: Colliding Cars In this problem we will consider the collision of two cars initially moving at right angles. We assume that after the collision the cars stick together and travel off as a single unit. The collision is therefore completely inelastic. Two cars of masses and collide at an intersection. Before the collision, car 1 was traveling eastward at a speed of , and car 2 was traveling northward at a speed of . After the collision, the two cars stick together and travel off in the direction shown. Part A p1 + p2 $ p $ p1p2 −−−− ” p1 +p2 $ p $ p1+p2 2 p1 + p2 $ p $ |p1 − p2 | p1 + p2 $ p $ p1 + 2 p2 2 −−−−−−−  m1 m2 v1 v2 First, find the magnitude of , that is, the speed of the two-car unit after the collision. Express in terms of , , and the cars’ initial speeds and . You did not open hints for this part. ANSWER: Part B Find the tangent of the angle . Express your answer in terms of the momenta of the two cars, and . ANSWER: Part C Suppose that after the collision, ; in other words, is . This means that before the collision: ANSWER: v v v m1 m2 v1 v2 v = p1 p2 tan( ) = tan = 1 45′ The magnitudes of the momenta of the cars were equal. The masses of the cars were equal. The velocities of the cars were equal. ± Catching a Ball on Ice Olaf is standing on a sheet of ice that covers the football stadium parking lot in Buffalo, New York; there is negligible friction between his feet and the ice. A friend throws Olaf a ball of mass 0.400 that is traveling horizontally at 11.2 . Olaf’s mass is 67.1 . Part A If Olaf catches the ball, with what speed do Olaf and the ball move afterward? Express your answer numerically in meters per second. You did not open hints for this part. ANSWER: Part B kg m/s kg vf vf = m/s If the ball hits Olaf and bounces off his chest horizontally at 8.00 in the opposite direction, what is his speed after the collision? Express your answer numerically in meters per second. You did not open hints for this part. ANSWER: A One-Dimensional Inelastic Collision Block 1, of mass = 2.90 , moves along a frictionless air track with speed = 25.0 . It collides with block 2, of mass = 17.0 , which was initially at rest. The blocks stick together after the collision. Part A Find the magnitude of the total initial momentum of the two-block system. Express your answer numerically. m/s vf vf = m/s m1 kg v1 m/s m2 kg pi You did not open hints for this part. ANSWER: Part B Find , the magnitude of the final velocity of the two-block system. Express your answer numerically. You did not open hints for this part. ANSWER: Score Summary: Your score on this assignment is 0%. You received 0 out of a possible total of 0 points. pi = kg  m/s vf vf = m/s

Chapter 9 Practice Problems (Practice – no credit) Due: 11:59pm on Friday, April 18, 2014 You will receive no credit for items you complete after the assignment is due. Grading Policy Momentum and Internal Forces Learning Goal: To understand the concept of total momentum for a system of objects and the effect of the internal forces on the total momentum. We begin by introducing the following terms: System: Any collection of objects, either pointlike or extended. In many momentum-related problems, you have a certain freedom in choosing the objects to be considered as your system. Making a wise choice is often a crucial step in solving the problem. Internal force: Any force interaction between two objects belonging to the chosen system. Let us stress that both interacting objects must belong to the system. External force: Any force interaction between objects at least one of which does not belong to the chosen system; in other words, at least one of the objects is external to the system. Closed system: a system that is not subject to any external forces. Total momentum: The vector sum of the individual momenta of all objects constituting the system. In this problem, you will analyze a system composed of two blocks, 1 and 2, of respective masses and . To simplify the analysis, we will make several assumptions: The blocks can move in only one dimension, namely, 1. along the x axis. 2. The masses of the blocks remain constant. 3. The system is closed. At time , the x components of the velocity and the acceleration of block 1 are denoted by and . Similarly, the x components of the velocity and acceleration of block 2 are denoted by and . In this problem, you will show that the total momentum of the system is not changed by the presence of internal forces. m1 m2 t v1(t) a1 (t) v2 (t) a2 (t) Part A Find , the x component of the total momentum of the system at time . Express your answer in terms of , , , and . ANSWER: Part B Find the time derivative of the x component of the system’s total momentum. Express your answer in terms of , , , and . You did not open hints for this part. ANSWER: Why did we bother with all this math? The expression for the derivative of momentum that we just obtained will be useful in reaching our desired conclusion, if only for this very special case. Part C The quantity (mass times acceleration) is dimensionally equivalent to which of the following? ANSWER: p(t) t m1 m2 v1 (t) v2 (t) p(t) = dp(t)/dt a1 (t) a2 (t) m1 m2 dp(t)/dt = ma Part D Acceleration is due to which of the following physical quantities? ANSWER: Part E Since we have assumed that the system composed of blocks 1 and 2 is closed, what could be the reason for the acceleration of block 1? You did not open hints for this part. ANSWER: momentum energy force acceleration inertia velocity speed energy momentum force Part F This question will be shown after you complete previous question(s). Part G Let us denote the x component of the force exerted by block 1 on block 2 by , and the x component of the force exerted by block 2 on block 1 by . Which of the following pairs equalities is a direct consequence of Newton’s second law? ANSWER: Part H Let us recall that we have denoted the force exerted by block 1 on block 2 by , and the force exerted by block 2 on block 1 by . If we suppose that is greater than , which of the following statements about forces is true? You did not open hints for this part. the large mass of block 1 air resistance Earth’s gravitational attraction a force exerted by block 2 on block 1 a force exerted by block 1 on block 2 F12 F21 and and and and F12 = m2a2 F21 = m1a1 F12 = m1a1 F21 = m2a2 F12 = m1a2 F21 = m2a1 F12 = m2a1 F21 = m1a2 F12 F21 m1 m2 ANSWER: Part I Now recall the expression for the time derivative of the x component of the system’s total momentum: . Considering the information that you now have, choose the best alternative for an equivalent expression to . You did not open hints for this part. ANSWER: Impulse and Momentum Ranking Task Six automobiles are initially traveling at the indicated velocities. The automobiles have different masses and velocities. The drivers step on the brakes and all automobiles are brought to rest. Part A Rank these automobiles based on the magnitude of their momentum before the brakes are applied, from largest to smallest. Rank from largest to smallest. To rank items as equivalent, overlap them. If the ranking cannot be determined, check the box below. ANSWER: Both forces have equal magnitudes. |F12 | > |F21| |F21 | > |F12| dpx(t)/dt = Fx dpx(t)/dt 0 nonzero constant kt kt2 Part B Rank these automobiles based on the magnitude of the impulse needed to stop them, from largest to smallest. Rank from largest to smallest. To rank items as equivalent, overlap them. If the ranking cannot be determined, check the box below. You did not open hints for this part. ANSWER: Part C Rank the automobiles based on the magnitude of the force needed to stop them, from largest to smallest. Rank from largest to smallest. To rank items as equivalent, overlap them. If the ranking cannot be determined, check the box below. You did not open hints for this part. ANSWER: A Game of Frictionless Catch Chuck and Jackie stand on separate carts, both of which can slide without friction. The combined mass of Chuck and his cart, , is identical to the combined mass of Jackie and her cart. Initially, Chuck and Jackie and their carts are at rest. Chuck then picks up a ball of mass and throws it to Jackie, who catches it. Assume that the ball travels in a straight line parallel to the ground (ignore the effect of gravity). After Chuck throws the ball, his speed relative to the ground is . The speed of the thrown ball relative to the ground is . Jackie catches the ball when it reaches her, and she and her cart begin to move. Jackie’s speed relative to the ground after she catches the ball is . When answering the questions in this problem, keep the following in mind: The original mass of Chuck and his cart does not include the 1. mass of the ball. 2. The speed of an object is the magnitude of its velocity. An object’s speed will always be a nonnegative quantity. mcart mball vc vb vj mcart Part A Find the relative speed between Chuck and the ball after Chuck has thrown the ball. Express the speed in terms of and . You did not open hints for this part. ANSWER: Part B What is the speed of the ball (relative to the ground) while it is in the air? Express your answer in terms of , , and . You did not open hints for this part. ANSWER: Part C What is Chuck’s speed (relative to the ground) after he throws the ball? Express your answer in terms of , , and . u vc vb u = vb mball mcart u vb = vc mball mcart u You did not open hints for this part. ANSWER: Part D Find Jackie’s speed (relative to the ground) after she catches the ball, in terms of . Express in terms of , , and . You did not open hints for this part. ANSWER: Part E Find Jackie’s speed (relative to the ground) after she catches the ball, in terms of . Express in terms of , , and . You did not open hints for this part. ANSWER: vc = vj vb vj mball mcart vb vj = vj u vj mball mcart u Momentum in an Explosion A giant “egg” explodes as part of a fireworks display. The egg is at rest before the explosion, and after the explosion, it breaks into two pieces, with the masses indicated in the diagram, traveling in opposite directions. Part A What is the momentum of piece A before the explosion? Express your answer numerically in kilogram meters per second. You did not open hints for this part. ANSWER: vj = pA,i Part B During the explosion, is the force of piece A on piece B greater than, less than, or equal to the force of piece B on piece A? You did not open hints for this part. ANSWER: Part C The momentum of piece B is measured to be 500 after the explosion. Find the momentum of piece A after the explosion. Enter your answer numerically in kilogram meters per second. You did not open hints for this part. ANSWER: pA,i = kg  m/s greater than less than equal to cannot be determined kg  m/s pA,f pA,f = kg  m/s ± PSS 9.1 Conservation of Momentum Learning Goal: To practice Problem-Solving Strategy 9.1 for conservation of momentum problems. An 80- quarterback jumps straight up in the air right before throwing a 0.43- football horizontally at 15 . How fast will he be moving backward just after releasing the ball? PROBLEM-SOLVING STRATEGY 9.1 Conservation of momentum MODEL: Clearly define the system. If possible, choose a system that is isolated ( ) or within which the interactions are sufficiently short and intense that you can ignore external forces for the duration of the interaction (the impulse approximation). Momentum is conserved. If it is not possible to choose an isolated system, try to divide the problem into parts such that momentum is conserved during one segment of the motion. Other segments of the motion can be analyzed using Newton’s laws or, as you will learn later, conservation of energy. VISUALIZE: Draw a before-and-after pictorial representation. Define symbols that will be used in the problem, list known values, and identify what you are trying to find. SOLVE: The mathematical representation is based on the law of conservation of momentum: . In component form, this is ASSESS: Check that your result has the correct units, is reasonable, and answers the question. Model The interaction at study in this problem is the action of throwing the ball, performed by the quarterback while being off the ground. To apply conservation of momentum to this interaction, you will need to clearly define a system that is isolated or within which the impulse approximation can be applied. Part A Sort the following objects as part of the system or not. Drag the appropriate objects to their respective bins. ANSWER: kg kg m/s F = net 0 P = f P  i (pfx + ( + ( += ( + ( + ( + )1 pfx)2 pfx)3 pix)1 pix)2 pix)3 (pfy + ( + ( += ( + ( + ( + )1 pfy)2 pfy)3 piy)1 piy)2 piy)3 Part B This question will be shown after you complete previous question(s). Visualize Solve Part C This question will be shown after you complete previous question(s). Assess Part D This question will be shown after you complete previous question(s). Conservation of Momentum in Inelastic Collisions Learning Goal: To understand the vector nature of momentum in the case in which two objects collide and stick together. In this problem we will consider a collision of two moving objects such that after the collision, the objects stick together and travel off as a single unit. The collision is therefore completely inelastic. You have probably learned that “momentum is conserved” in an inelastic collision. But how does this fact help you to solve collision problems? The following questions should help you to clarify the meaning and implications of the statement “momentum is conserved.” Part A What physical quantities are conserved in this collision? ANSWER: Part B Two cars of equal mass collide inelastically and stick together after the collision. Before the collision, their speeds are and . What is the speed of the two-car system after the collision? the magnitude of the momentum only the net momentum (considered as a vector) only the momentum of each object considered individually v1 v2 You did not open hints for this part. ANSWER: Part C Two cars collide inelastically and stick together after the collision. Before the collision, the magnitudes of their momenta are and . After the collision, what is the magnitude of their combined momentum? You did not open hints for this part. ANSWER: The answer depends on the directions in which the cars were moving before the collision. v1 + v2 v1 − v2 v2 − v1 v1v2 −−−− ” v1+v2 2 v1 + 2 v2 2 −−−−−−−  p1 p2 Part D Two cars collide inelastically and stick together after the collision. Before the collision, their momenta are and . After the collision, their combined momentum is . Of what can one be certain? You did not open hints for this part. ANSWER: Part E Two cars collide inelastically and stick together after the collision. Before the collision, the magnitudes of their momenta are and . After the collision, the magnitude of their combined momentum is . Of what can one be certain? The answer depends on the directions in which the cars were moving before the collision. p1 + p2 p1 − p2 p2 − p1 p1p2 −−−− ” p1+p2 2 p1 + 2 p2 2 −−−−−−−  p 1 p 2 p p = p1 + # p2 # p = p1 − # p2 # p = p2 − # p1 # p1 p2 p You did not open hints for this part. ANSWER: Colliding Cars In this problem we will consider the collision of two cars initially moving at right angles. We assume that after the collision the cars stick together and travel off as a single unit. The collision is therefore completely inelastic. Two cars of masses and collide at an intersection. Before the collision, car 1 was traveling eastward at a speed of , and car 2 was traveling northward at a speed of . After the collision, the two cars stick together and travel off in the direction shown. Part A p1 + p2 $ p $ p1p2 −−−− ” p1 +p2 $ p $ p1+p2 2 p1 + p2 $ p $ |p1 − p2 | p1 + p2 $ p $ p1 + 2 p2 2 −−−−−−−  m1 m2 v1 v2 First, find the magnitude of , that is, the speed of the two-car unit after the collision. Express in terms of , , and the cars’ initial speeds and . You did not open hints for this part. ANSWER: Part B Find the tangent of the angle . Express your answer in terms of the momenta of the two cars, and . ANSWER: Part C Suppose that after the collision, ; in other words, is . This means that before the collision: ANSWER: v v v m1 m2 v1 v2 v = p1 p2 tan( ) = tan = 1 45′ The magnitudes of the momenta of the cars were equal. The masses of the cars were equal. The velocities of the cars were equal. ± Catching a Ball on Ice Olaf is standing on a sheet of ice that covers the football stadium parking lot in Buffalo, New York; there is negligible friction between his feet and the ice. A friend throws Olaf a ball of mass 0.400 that is traveling horizontally at 11.2 . Olaf’s mass is 67.1 . Part A If Olaf catches the ball, with what speed do Olaf and the ball move afterward? Express your answer numerically in meters per second. You did not open hints for this part. ANSWER: Part B kg m/s kg vf vf = m/s If the ball hits Olaf and bounces off his chest horizontally at 8.00 in the opposite direction, what is his speed after the collision? Express your answer numerically in meters per second. You did not open hints for this part. ANSWER: A One-Dimensional Inelastic Collision Block 1, of mass = 2.90 , moves along a frictionless air track with speed = 25.0 . It collides with block 2, of mass = 17.0 , which was initially at rest. The blocks stick together after the collision. Part A Find the magnitude of the total initial momentum of the two-block system. Express your answer numerically. m/s vf vf = m/s m1 kg v1 m/s m2 kg pi You did not open hints for this part. ANSWER: Part B Find , the magnitude of the final velocity of the two-block system. Express your answer numerically. You did not open hints for this part. ANSWER: Score Summary: Your score on this assignment is 0%. You received 0 out of a possible total of 0 points. pi = kg  m/s vf vf = m/s

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Name Tutorials in Introductory Physics ©Pearson Custom Publishing McDermott, Shaffer, & P.E.G., U. Wash. Updated Preliminary Second Edition, 2011 Mech HW–39 1. A block initially at rest is given a quick push by a hand. The block slides across the floor, gradually slows down, and comes to rest. a. In the spaces provided, draw and label separate free-body diagrams for the block at each of the three instants shown. A quick push by a hand… 1. (Initially at rest) the sliding block slows… 2. v and is finally at rest. 3. b. Rank the magnitudes of all the horizontal forces in the diagram for instant 1. Explain. c. Are any of the forces that you drew for instant 1 missing from your diagram for instant 2? If so, for each force that is missing, explain how you knew to include the force on the first diagram but not on the second. d. Are any of the forces that you drew for instant 1 missing from your diagram for instant 3? If so, for each force that is missing, explain how you knew to include the force on the first diagram but not on the third. NEWTON’S SECOND AND THIRD LAWS Newton’s second and third laws Tutorials in Introductory Physics ©Pearson Custom Publishing McDermott, Shaffer, & P.E.G., U. Wash. Updated Preliminary Second Edition, 2011 Mech HW–40 2. Two crates, A and B, are in an elevator as shown. The mass of crate A is greater than the mass of crate B. a. The elevator moves downward at constant speed. i. How does the acceleration of crate A compare to that of crate B? Explain. ii. In the spaces provided below, draw and label separate free-body diagrams for the crates. Free-body diagram for crate A Free-body diagram for crate B iii. Rank the forces on the crates according to magnitude, from largest to smallest. Explain your reasoning, including how you used Newton’s second and third laws. iv. In the spaces provided at right, draw arrows to indicate the direction of the net force on each crate. If the net force on either crate is zero, state so explicitly. Explain. Is the magnitude of the net force on crate A greater than, less than, or equal to that on crate B? Explain. Elevator (moving down at constant speed) A B Cable Crate A Crate B Direction of net force Newton’s second and third laws Name Tutorials in Introductory Physics ©Pearson Custom Publishing McDermott, Shaffer, & P.E.G., U. Wash. Updated Preliminary Second Edition, 2011 Mech HW–41 b. As the elevator approaches its destination, its speed decreases. (It continues to move downward.) i. How does the acceleration of crate A compare to that of crate B? Explain. ii. In the spaces provided below, draw and label separate free-body diagrams for the crates in this case. Free-body diagram for crate A Free-body diagram for crate B iii. Rank the forces on the crates according to magnitude, from largest to smallest. Explain your reasoning, including how you used Newton’s second and third laws. iv. In the spaces provided at right, draw arrows to indicate the direction of the net force on each crate. If the net force on either crate is zero, state so explicitly. Explain. Is the magnitude of the net force on crate A greater than, less than, or equal to that on crate B? Explain. Crate A Crate B Direction of net force Newton’s second and third laws Tutorials in Introductory Physics ©Pearson Custom Publishing McDermott, Shaffer, & P.E.G., U. Wash. Updated Preliminary Second Edition, 2011 Mech HW–42 3. A hand pushes three identical bricks as shown. The bricks are moving to the left and speeding up. System A consists of two bricks stacked together. System B consists of a single brick. System C consists of all three bricks. There is friction between the bricks and the table. a. In the spaces provided at right, draw and label separate free-body diagrams for systems A and B. b. The vector representing the acceleration of system A is shown at right. Draw the acceleration vectors for systems B and C using the same scale. Explain. c. The vector representing the net force on system A is shown at right. Draw the net force vectors for systems B and C using the same scale. Explain. d. The vector representing the frictional force on system A is shown below. Draw the remaining force vectors using the same scale. NBH NAB NBA fAT fBT Explain how you knew to draw the force vectors as you did. A B Free-body diagram for system A Free-body diagram for system B Acceleration of A Acceleration of B Acceleration of C Net force on A Net force on B Net force on C

Name Tutorials in Introductory Physics ©Pearson Custom Publishing McDermott, Shaffer, & P.E.G., U. Wash. Updated Preliminary Second Edition, 2011 Mech HW–39 1. A block initially at rest is given a quick push by a hand. The block slides across the floor, gradually slows down, and comes to rest. a. In the spaces provided, draw and label separate free-body diagrams for the block at each of the three instants shown. A quick push by a hand… 1. (Initially at rest) the sliding block slows… 2. v and is finally at rest. 3. b. Rank the magnitudes of all the horizontal forces in the diagram for instant 1. Explain. c. Are any of the forces that you drew for instant 1 missing from your diagram for instant 2? If so, for each force that is missing, explain how you knew to include the force on the first diagram but not on the second. d. Are any of the forces that you drew for instant 1 missing from your diagram for instant 3? If so, for each force that is missing, explain how you knew to include the force on the first diagram but not on the third. NEWTON’S SECOND AND THIRD LAWS Newton’s second and third laws Tutorials in Introductory Physics ©Pearson Custom Publishing McDermott, Shaffer, & P.E.G., U. Wash. Updated Preliminary Second Edition, 2011 Mech HW–40 2. Two crates, A and B, are in an elevator as shown. The mass of crate A is greater than the mass of crate B. a. The elevator moves downward at constant speed. i. How does the acceleration of crate A compare to that of crate B? Explain. ii. In the spaces provided below, draw and label separate free-body diagrams for the crates. Free-body diagram for crate A Free-body diagram for crate B iii. Rank the forces on the crates according to magnitude, from largest to smallest. Explain your reasoning, including how you used Newton’s second and third laws. iv. In the spaces provided at right, draw arrows to indicate the direction of the net force on each crate. If the net force on either crate is zero, state so explicitly. Explain. Is the magnitude of the net force on crate A greater than, less than, or equal to that on crate B? Explain. Elevator (moving down at constant speed) A B Cable Crate A Crate B Direction of net force Newton’s second and third laws Name Tutorials in Introductory Physics ©Pearson Custom Publishing McDermott, Shaffer, & P.E.G., U. Wash. Updated Preliminary Second Edition, 2011 Mech HW–41 b. As the elevator approaches its destination, its speed decreases. (It continues to move downward.) i. How does the acceleration of crate A compare to that of crate B? Explain. ii. In the spaces provided below, draw and label separate free-body diagrams for the crates in this case. Free-body diagram for crate A Free-body diagram for crate B iii. Rank the forces on the crates according to magnitude, from largest to smallest. Explain your reasoning, including how you used Newton’s second and third laws. iv. In the spaces provided at right, draw arrows to indicate the direction of the net force on each crate. If the net force on either crate is zero, state so explicitly. Explain. Is the magnitude of the net force on crate A greater than, less than, or equal to that on crate B? Explain. Crate A Crate B Direction of net force Newton’s second and third laws Tutorials in Introductory Physics ©Pearson Custom Publishing McDermott, Shaffer, & P.E.G., U. Wash. Updated Preliminary Second Edition, 2011 Mech HW–42 3. A hand pushes three identical bricks as shown. The bricks are moving to the left and speeding up. System A consists of two bricks stacked together. System B consists of a single brick. System C consists of all three bricks. There is friction between the bricks and the table. a. In the spaces provided at right, draw and label separate free-body diagrams for systems A and B. b. The vector representing the acceleration of system A is shown at right. Draw the acceleration vectors for systems B and C using the same scale. Explain. c. The vector representing the net force on system A is shown at right. Draw the net force vectors for systems B and C using the same scale. Explain. d. The vector representing the frictional force on system A is shown below. Draw the remaining force vectors using the same scale. NBH NAB NBA fAT fBT Explain how you knew to draw the force vectors as you did. A B Free-body diagram for system A Free-body diagram for system B Acceleration of A Acceleration of B Acceleration of C Net force on A Net force on B Net force on C

Question 1, chap 33, sect 3. part 1 of 2 10 points The compound eyes of bees and other insects are highly sensitive to light in the ultraviolet portion of the spectrum, particularly light with frequencies between 7.5 × 1014 Hz and 1.0 × 1015 Hz. The speed of light is 3 × 108 m/s. What is the largest wavelength to which these frequencies correspond? Question 3, chap 33, sect 3. part 1 of 3 10 points A plane electromagnetic sinusoidal wave of frequency 10.7 MHz travels in free space. The speed of light is 2.99792 × 108 m/s. Determine the wavelength of the wave. Question 4, chap 33, sect 3. part 2 of 3 10 points Find the period of the wave. Question 2, chap 33, sect 3. part 2 of 2 10 points What is the smallest wavelength? Question 5, chap 33, sect 3. part 3 of 3 10 points At some point and some instant, the electric field has has a value of 998 N/C. Calculate the magnitude of the magnetic field at this point and this instant. Question 6, chap 33, sect 3. part 1 of 2 10 points A plane electromagnetic sinusoidal wave of frequency 10.7 MHz travels in free space. The speed of light is 2.99792 × 108 m/s. Determine the wavelength of the wave. Question 8, chap 33, sect 3. part 1 of 1 10 points The magnetic field amplitude of an electromagnetic wave is 9.9 × 10−6 T. The speed of light is 2.99792 × 108 m/s . Calculate the amplitude of the electric field if the wave is traveling in free space. Question 7, chap 33, sect 3. part 2 of 2 10 points At some point and some instant, the electric field has has a value of 998 V/m. Calculate the magnitude of the magnetic field at this point and this instant. Question 9, chap 33, sect 5. part 1 of 1 10 points The cable is carrying the current I(t). at the surface of a long transmission cable of resistivity ρ, length ℓ and radius a, using the expression ~S = 1 μ0 ~E × ~B . Question 10, chap 33, sect 5. part 1 of 1 10 points In 1965 Penzias and Wilson discovered the cosmic microwave radiation left over from the Big Bang expansion of the universe. The energy density of this radiation is 7.64 × 10−14 J/m3. The speed of light 2.99792 × 108 m/s and the permeability of free space is 4π × 10−7 N/A2. Determine the corresponding electric field amplQuestion 11, chap 33, sect 5. part 1 of 5 10 points Consider a monochromatic electromagnetic plane wave propagating in the x direction. At a particular point in space, the magnitude of the electric field has an instantaneous value of 998 V/m in the positive y-direction. The wave is traveling in the positive x-direction. x y z E wave propagation The speed of light is 2.99792×108 m/s, the permeability of free space is 4π×10−7 T ・ N/A and the permittivity of free space 8.85419 × 10−12 C2/N ・ m2. Compute the instantaneous magnitude of the magnetic field at the same point and time.itude. Question 12, chap 33, sect 5. part 2 of 5 10 points What is the instantaneous magnitude of the Poynting vector at the same point and time? Question 13, chap 33, sect 5. part 3 of 5 10 points What are the directions of the instantaneous magnetic field and theQuestion 14, chap 33, sect 5. part 4 of 5 10 points What is the instantaneous value of the energy density of the electric field? Question 16, chap 33, sect 6. part 1 of 4 10 points Consider an electromagnetic plane wave with time average intensity 104 W/m2 . The speed of light is 2.99792 × 108 m/s and the permeability of free space is 4 π × 10−7 T・m/A. What is its maximum electric field? What is the instantaneous value of the energy density of the magnetic field? Question 17, chap 33, sect 6. part 2 of 4 10 points What is the the maximum magnetic field? Question 19, chap 33, sect 6. part 4 of 4 10 points Consider an electromagnetic wave pattern as shown in the figure below. Question 18, chap 33, sect 6. part 3 of 4 10 points What is the pressure on a surface which is perpendicular to the beam and is totally reflective? Question 20, chap 33, sect 8. part 1 of 1 10 points A coin is at the bottom of a beaker. The beaker is filled with 1.6 cm of water (n1 = 1.33) covered by 2.1 cm of liquid (n2 = 1.4) floating on the water. How deep does the coin appear to be from the upper surface of the liquid (near the top of the beaker)? An cylindrical opaque drinking glass has a diameter 3 cm and height h, as shown in the figure. An observer’s eye is placed as shown (the observer is just barely looking over the rim of the glass). When empty, the observer can just barely see the edge of the bottom of the glass. When filled to the brim with a transparent liquid, the observer can just barely see the center of the bottom of the glass. The liquid in the drinking glass has an index of refraction of 1.4 . θi h d θr eye Calculate the angle θr . Question 22, chap 33, sect 8. part 2 of 2 10 points Calculate the height h of the glass.

Question 1, chap 33, sect 3. part 1 of 2 10 points The compound eyes of bees and other insects are highly sensitive to light in the ultraviolet portion of the spectrum, particularly light with frequencies between 7.5 × 1014 Hz and 1.0 × 1015 Hz. The speed of light is 3 × 108 m/s. What is the largest wavelength to which these frequencies correspond? Question 3, chap 33, sect 3. part 1 of 3 10 points A plane electromagnetic sinusoidal wave of frequency 10.7 MHz travels in free space. The speed of light is 2.99792 × 108 m/s. Determine the wavelength of the wave. Question 4, chap 33, sect 3. part 2 of 3 10 points Find the period of the wave. Question 2, chap 33, sect 3. part 2 of 2 10 points What is the smallest wavelength? Question 5, chap 33, sect 3. part 3 of 3 10 points At some point and some instant, the electric field has has a value of 998 N/C. Calculate the magnitude of the magnetic field at this point and this instant. Question 6, chap 33, sect 3. part 1 of 2 10 points A plane electromagnetic sinusoidal wave of frequency 10.7 MHz travels in free space. The speed of light is 2.99792 × 108 m/s. Determine the wavelength of the wave. Question 8, chap 33, sect 3. part 1 of 1 10 points The magnetic field amplitude of an electromagnetic wave is 9.9 × 10−6 T. The speed of light is 2.99792 × 108 m/s . Calculate the amplitude of the electric field if the wave is traveling in free space. Question 7, chap 33, sect 3. part 2 of 2 10 points At some point and some instant, the electric field has has a value of 998 V/m. Calculate the magnitude of the magnetic field at this point and this instant. Question 9, chap 33, sect 5. part 1 of 1 10 points The cable is carrying the current I(t). at the surface of a long transmission cable of resistivity ρ, length ℓ and radius a, using the expression ~S = 1 μ0 ~E × ~B . Question 10, chap 33, sect 5. part 1 of 1 10 points In 1965 Penzias and Wilson discovered the cosmic microwave radiation left over from the Big Bang expansion of the universe. The energy density of this radiation is 7.64 × 10−14 J/m3. The speed of light 2.99792 × 108 m/s and the permeability of free space is 4π × 10−7 N/A2. Determine the corresponding electric field amplQuestion 11, chap 33, sect 5. part 1 of 5 10 points Consider a monochromatic electromagnetic plane wave propagating in the x direction. At a particular point in space, the magnitude of the electric field has an instantaneous value of 998 V/m in the positive y-direction. The wave is traveling in the positive x-direction. x y z E wave propagation The speed of light is 2.99792×108 m/s, the permeability of free space is 4π×10−7 T ・ N/A and the permittivity of free space 8.85419 × 10−12 C2/N ・ m2. Compute the instantaneous magnitude of the magnetic field at the same point and time.itude. Question 12, chap 33, sect 5. part 2 of 5 10 points What is the instantaneous magnitude of the Poynting vector at the same point and time? Question 13, chap 33, sect 5. part 3 of 5 10 points What are the directions of the instantaneous magnetic field and theQuestion 14, chap 33, sect 5. part 4 of 5 10 points What is the instantaneous value of the energy density of the electric field? Question 16, chap 33, sect 6. part 1 of 4 10 points Consider an electromagnetic plane wave with time average intensity 104 W/m2 . The speed of light is 2.99792 × 108 m/s and the permeability of free space is 4 π × 10−7 T・m/A. What is its maximum electric field? What is the instantaneous value of the energy density of the magnetic field? Question 17, chap 33, sect 6. part 2 of 4 10 points What is the the maximum magnetic field? Question 19, chap 33, sect 6. part 4 of 4 10 points Consider an electromagnetic wave pattern as shown in the figure below. Question 18, chap 33, sect 6. part 3 of 4 10 points What is the pressure on a surface which is perpendicular to the beam and is totally reflective? Question 20, chap 33, sect 8. part 1 of 1 10 points A coin is at the bottom of a beaker. The beaker is filled with 1.6 cm of water (n1 = 1.33) covered by 2.1 cm of liquid (n2 = 1.4) floating on the water. How deep does the coin appear to be from the upper surface of the liquid (near the top of the beaker)? An cylindrical opaque drinking glass has a diameter 3 cm and height h, as shown in the figure. An observer’s eye is placed as shown (the observer is just barely looking over the rim of the glass). When empty, the observer can just barely see the edge of the bottom of the glass. When filled to the brim with a transparent liquid, the observer can just barely see the center of the bottom of the glass. The liquid in the drinking glass has an index of refraction of 1.4 . θi h d θr eye Calculate the angle θr . Question 22, chap 33, sect 8. part 2 of 2 10 points Calculate the height h of the glass.