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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WEEKLY ASSIGNMENT #5 (WOW THAT TOOK A WHILE) NAME: 1. Find the linear approximation of the function f(x; y; z) = p x2 + y2 + z2 at some point to approximate a value of the number p (3:02)2 + (1:97)2 + (5:99)2. 1 2. Consider your favorite function, the Cobb-Douglas production function. P(L;K) = 1:5L:65K:35 modeling the production of the state of Idaho. Over time we discover that capitol is gradually increasing at an approximate rate of 0:02 units per year. If we decide as a group that we are perfectly happy with our production level and would rather have additional vacation time then how much can we decrease labor by each year and keep the same level of production. In how long(rounded up to the nearest year) will we have an additional week of vacation? 2 3. Use the chain rule to find dz dt or dw=dt (a) z = x?y x+2y x = et; y = e?t. (b) w = sin x cos x x = p t; y = 1=t. 4. Use the chain rule to find @z=@t or @z=@s (a) z = (x ? y)5 x = s2t; y = st2 (b) z = er cos  r = st;  = p x2 + y2. 3 5. The temperature at a point (x; y; z) is given by the function T(x; y; z) = 200e?x2?3y2?9z2 where T is measure in C and x; y; z in meters. (a) Find the rate of change of temperature at the point (2;?1; 2) in the direction toward the point (3;?3; 3). (b) In which direction does the temperature increase fastest, and what is that fastest rate? 4 6. Suppose (1; 1) is a critical point of a function f with continuous second derivatives. In each case, what can you say about f. (a) fxx(1; 1) = 4; fxy(1; 1) = 1; fyy(1; 1) = 2 (b) fxx(1; 1) = 4; fxy(1; 1) = 3; fyy(1; 1) = 2 (c) fxx(1; 1) = ?1; fxy(1; 1) = 6; fyy(1; 1) = 1 (d) fxx(1; 1) = ?1; fxy(1; 1) = 2; fyy(1; 1) = ?8 (e) fxx(1; 1) = 4; fxy(1; 1) = 6; fyy(1; 1) = 9 5 Bonus Show that f(x; y) = x2 + 4y2 ? 4xy + 2 has an infinite number of critical points, and for all of them D = 0 at each one. Then show that f has a local (and absolute) minimum at each critical point. 6

WEEKLY ASSIGNMENT #5 (WOW THAT TOOK A WHILE) NAME: 1. Find the linear approximation of the function f(x; y; z) = p x2 + y2 + z2 at some point to approximate a value of the number p (3:02)2 + (1:97)2 + (5:99)2. 1 2. Consider your favorite function, the Cobb-Douglas production function. P(L;K) = 1:5L:65K:35 modeling the production of the state of Idaho. Over time we discover that capitol is gradually increasing at an approximate rate of 0:02 units per year. If we decide as a group that we are perfectly happy with our production level and would rather have additional vacation time then how much can we decrease labor by each year and keep the same level of production. In how long(rounded up to the nearest year) will we have an additional week of vacation? 2 3. Use the chain rule to find dz dt or dw=dt (a) z = x?y x+2y x = et; y = e?t. (b) w = sin x cos x x = p t; y = 1=t. 4. Use the chain rule to find @z=@t or @z=@s (a) z = (x ? y)5 x = s2t; y = st2 (b) z = er cos  r = st;  = p x2 + y2. 3 5. The temperature at a point (x; y; z) is given by the function T(x; y; z) = 200e?x2?3y2?9z2 where T is measure in C and x; y; z in meters. (a) Find the rate of change of temperature at the point (2;?1; 2) in the direction toward the point (3;?3; 3). (b) In which direction does the temperature increase fastest, and what is that fastest rate? 4 6. Suppose (1; 1) is a critical point of a function f with continuous second derivatives. In each case, what can you say about f. (a) fxx(1; 1) = 4; fxy(1; 1) = 1; fyy(1; 1) = 2 (b) fxx(1; 1) = 4; fxy(1; 1) = 3; fyy(1; 1) = 2 (c) fxx(1; 1) = ?1; fxy(1; 1) = 6; fyy(1; 1) = 1 (d) fxx(1; 1) = ?1; fxy(1; 1) = 2; fyy(1; 1) = ?8 (e) fxx(1; 1) = 4; fxy(1; 1) = 6; fyy(1; 1) = 9 5 Bonus Show that f(x; y) = x2 + 4y2 ? 4xy + 2 has an infinite number of critical points, and for all of them D = 0 at each one. Then show that f has a local (and absolute) minimum at each critical point. 6

Sex, Gender, and Popular Culture Spring 2015 Look through popular magazines, and see if you can find advertisements that objectify women in order to sell a product. Alternately, you may use an advertisement on television (but make sure to provide a link to the ad so I can see it!). Study these images then write a paper about objectification that deals with all or some of the following: • What effect(s), if any, do you think the objectification of women’s bodies has on our culture? • Jean Kilbourne states “turning a human being into a thing is almost always the first step toward justifying violence against that person.” What do you think she means by this? Do you agree with her reasoning? Why or why not? • Some people would argue that depicting a woman’s body as an object is a form of art. What is your opinion of this point of view? Explain your reasoning. • Why do you think that women are objectified more often than men are? • How does sexualization and objectification play out differently across racial lines? • Kilbourne explains that the consequences of being objectified are different – and more serious – for women than for men. Do you agree? How is the world different for women than it is for men? How do objectified images of women interact with those in our culture differently from the way images of men do? Why is it important to look at images in the context of the culture? • What is the difference between sexual objectification and sexual subjectification? (Ros Gill ) • How do ads construct violent white masculinity and how does that vision of masculinity hurt both men and women? Throughout your written analysis, be sure to make clear and specific reference to the images you selected, and please submit these images with your paper. Make sure you engage with and reference to at least 4 of the following authors: Kilbourne, Bordo, Hunter & Soto, Rose, Durham, Gill, Katz, Schuchardt, Ono and Buescher. Guidelines:  Keep your content focused on structural, systemic, institutional factors rather than the individual: BE ANALYTICAL NOT ANECDOTAL.  Avoid using the first person or including personal stories/reactions. You must make sure to actively engage with your readings: these essays need to be informed and framed by the theoretical material you have been reading this semester.  Keep within the 4-6 page limit; use 12-point font, double spacing and 1-inch margins.  Use formal writing conventions (introduction/thesis statement, body, conclusion) and correct grammar. Resources may be cited within the text of your paper, i.e. (Walters, 2013).

Sex, Gender, and Popular Culture Spring 2015 Look through popular magazines, and see if you can find advertisements that objectify women in order to sell a product. Alternately, you may use an advertisement on television (but make sure to provide a link to the ad so I can see it!). Study these images then write a paper about objectification that deals with all or some of the following: • What effect(s), if any, do you think the objectification of women’s bodies has on our culture? • Jean Kilbourne states “turning a human being into a thing is almost always the first step toward justifying violence against that person.” What do you think she means by this? Do you agree with her reasoning? Why or why not? • Some people would argue that depicting a woman’s body as an object is a form of art. What is your opinion of this point of view? Explain your reasoning. • Why do you think that women are objectified more often than men are? • How does sexualization and objectification play out differently across racial lines? • Kilbourne explains that the consequences of being objectified are different – and more serious – for women than for men. Do you agree? How is the world different for women than it is for men? How do objectified images of women interact with those in our culture differently from the way images of men do? Why is it important to look at images in the context of the culture? • What is the difference between sexual objectification and sexual subjectification? (Ros Gill ) • How do ads construct violent white masculinity and how does that vision of masculinity hurt both men and women? Throughout your written analysis, be sure to make clear and specific reference to the images you selected, and please submit these images with your paper. Make sure you engage with and reference to at least 4 of the following authors: Kilbourne, Bordo, Hunter & Soto, Rose, Durham, Gill, Katz, Schuchardt, Ono and Buescher. Guidelines:  Keep your content focused on structural, systemic, institutional factors rather than the individual: BE ANALYTICAL NOT ANECDOTAL.  Avoid using the first person or including personal stories/reactions. You must make sure to actively engage with your readings: these essays need to be informed and framed by the theoretical material you have been reading this semester.  Keep within the 4-6 page limit; use 12-point font, double spacing and 1-inch margins.  Use formal writing conventions (introduction/thesis statement, body, conclusion) and correct grammar. Resources may be cited within the text of your paper, i.e. (Walters, 2013).

The objectification of women has been a very controversial topic … Read More...
Essay list

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Fall Semester 2015 NMSU Econ 252, Instructor: Dr. Larry Blank Writing Assignment and Critical Thinking Problems: This assignment is worth 100 points toward your overall course average. The criteria used to grade this assignment includes the professional appearance of the document you submit, your ability to use the principles of supply and demand to critically assess the impacts, and your ability to explain your conclusions in writing. Each part can be answered in one page or less. Assigned: October 5, 2015 Deadline: Friday, October 16, 2015 You will email your assignment in Canvas. Before you email your assignment, make sure your name is on your paper AND your full name is included in the electronic file name. For example, filename: Jose Sanchez_Econ252_paper.doc I will not read your work if your name is not in the electronic filename. Assignment: Answers to all parts shall be completed in a Microsoft Word document. Begin by copying the Scenario below and then, for each part, copy the problem before completing your answer. You may want to draw your diagrams in Microsoft PowerPoint or other software and then copy and paste the diagram into the Word document as a “Picture (Enhanced Metafile)” using the “Paste Special” feature in Word. The document you turn in should be six (6) pages long. For the first page include a short title for this assignment, the course name and number, your name, and then copy and paste everything below beginning with “Scenario” onto your first page. The 2nd page of your document should include the description of Part 1 and then your diagram and answer. Do the same for Parts 2-5, with each part on a separate page. Scenario: The Federal Government implemented a policy some years ago to subsidize the production of ethanol fuel at 46 cents per gallon. See news article here: http://usnews.nbcnews.com/_news/2011/12/29/9804028-6-billion-a-year-ethanol-subsidy-dies-but-wait-theres-more?lite Ethanol is an alternative fuel (a substitute for regular gasoline) that can be used in some models of automobiles designed to burn any mix of gasoline up to 85% ethanol (fuel is known as E85, and auto manufacturers label these vehicles as “FlexFuel” and similar names). A primary input in the production of ethanol is corn. For the purposes of this assignment, assume that all relevant markets are perfectly competitive. Part 1: Show geometrically using the supply and demand curves the impact the subsidy had in the ethanol market (hint: the result has been a reduction in the market price of ethanol). Fully explain the impact of the production subsidy in terms of the behavior of producers (sellers) in the market and customers (buyers) in the market and what has happened to equilibrium price and quantity in the market for ethanol. Part 2: Show geometrically using the supply and demand curves what impact the reduction in market price for ethanol had in the market for regular gasoline. Fully explain the impact this reduced ethanol price had on the customer demand for regular gasoline. Part 3: Show geometrically using the supply and demand curves the impact due to the change in the equilibrium quantity in the market for ethanol had in the market for corn. Fully explain the impact and the resulting equilibrium price and quantity for corn. Part 4: Show geometrically using the supply and demand curves what impact the change in the market price of corn had in the market for manufactured corn tortillas (assume that the market for corn tortillas is perfectly competitive). Corn tortillas are a staple food item in the diets of millions of families across the U.S.. Fully explain the impact of change in the market price of corn in terms of the behavior of producers (sellers) in the market and customers (buyers) in the corn tortilla market. Part 5: Show geometrically using the supply and demand curves the impact in the ethanol market when the ethanol subsidy ended on Jan. 1, 2012. Give one possible explanation why I can no longer find E85 fuel at gas stations. Hint: When the subsidy still existed, the market price of E85 was about 30 cents a gallon less than regular gasoline. E85 is not a perfect substitute for regular gasoline because the performance is less and gas mileage drops by 5-7 miles per gallon.

Fall Semester 2015 NMSU Econ 252, Instructor: Dr. Larry Blank Writing Assignment and Critical Thinking Problems: This assignment is worth 100 points toward your overall course average. The criteria used to grade this assignment includes the professional appearance of the document you submit, your ability to use the principles of supply and demand to critically assess the impacts, and your ability to explain your conclusions in writing. Each part can be answered in one page or less. Assigned: October 5, 2015 Deadline: Friday, October 16, 2015 You will email your assignment in Canvas. Before you email your assignment, make sure your name is on your paper AND your full name is included in the electronic file name. For example, filename: Jose Sanchez_Econ252_paper.doc I will not read your work if your name is not in the electronic filename. Assignment: Answers to all parts shall be completed in a Microsoft Word document. Begin by copying the Scenario below and then, for each part, copy the problem before completing your answer. You may want to draw your diagrams in Microsoft PowerPoint or other software and then copy and paste the diagram into the Word document as a “Picture (Enhanced Metafile)” using the “Paste Special” feature in Word. The document you turn in should be six (6) pages long. For the first page include a short title for this assignment, the course name and number, your name, and then copy and paste everything below beginning with “Scenario” onto your first page. The 2nd page of your document should include the description of Part 1 and then your diagram and answer. Do the same for Parts 2-5, with each part on a separate page. Scenario: The Federal Government implemented a policy some years ago to subsidize the production of ethanol fuel at 46 cents per gallon. See news article here: http://usnews.nbcnews.com/_news/2011/12/29/9804028-6-billion-a-year-ethanol-subsidy-dies-but-wait-theres-more?lite Ethanol is an alternative fuel (a substitute for regular gasoline) that can be used in some models of automobiles designed to burn any mix of gasoline up to 85% ethanol (fuel is known as E85, and auto manufacturers label these vehicles as “FlexFuel” and similar names). A primary input in the production of ethanol is corn. For the purposes of this assignment, assume that all relevant markets are perfectly competitive. Part 1: Show geometrically using the supply and demand curves the impact the subsidy had in the ethanol market (hint: the result has been a reduction in the market price of ethanol). Fully explain the impact of the production subsidy in terms of the behavior of producers (sellers) in the market and customers (buyers) in the market and what has happened to equilibrium price and quantity in the market for ethanol. Part 2: Show geometrically using the supply and demand curves what impact the reduction in market price for ethanol had in the market for regular gasoline. Fully explain the impact this reduced ethanol price had on the customer demand for regular gasoline. Part 3: Show geometrically using the supply and demand curves the impact due to the change in the equilibrium quantity in the market for ethanol had in the market for corn. Fully explain the impact and the resulting equilibrium price and quantity for corn. Part 4: Show geometrically using the supply and demand curves what impact the change in the market price of corn had in the market for manufactured corn tortillas (assume that the market for corn tortillas is perfectly competitive). Corn tortillas are a staple food item in the diets of millions of families across the U.S.. Fully explain the impact of change in the market price of corn in terms of the behavior of producers (sellers) in the market and customers (buyers) in the corn tortilla market. Part 5: Show geometrically using the supply and demand curves the impact in the ethanol market when the ethanol subsidy ended on Jan. 1, 2012. Give one possible explanation why I can no longer find E85 fuel at gas stations. Hint: When the subsidy still existed, the market price of E85 was about 30 cents a gallon less than regular gasoline. E85 is not a perfect substitute for regular gasoline because the performance is less and gas mileage drops by 5-7 miles per gallon.

Assignment 8 Due: 11:59pm on Friday, April 4, 2014 You will receive no credit for items you complete after the assignment is due. Grading Policy Conceptual Question 10.3 Part A If a particle’s speed increases by a factor of 5, by what factor does its kinetic energy change? ANSWER: Correct Conceptual Question 10.11 A spring is compressed 1.5 . Part A How far must you compress a spring with twice the spring constant to store the same amount of energy? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct = 25 K2 K1 cm x = 1.1 cm Problem 10.2 The lowest point in Death Valley is below sea level. The summit of nearby Mt. Whitney has an elevation of 4420 . Part A What is the change in potential energy of an energetic 80 hiker who makes it from the floor of Death Valley to the top of Mt.Whitney? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Problem 10.3 Part A At what speed does a 1800 compact car have the same kinetic energy as a 1.80×104 truck going 21.0 ? Express your answer with the appropriate units. ANSWER: Correct Problem 10.5 A boy reaches out of a window and tosses a ball straight up with a speed of 13 . The ball is 21 above the ground as he releases it. 85m m kg U = 3.5×106 J kg kg km/hr vc = 66.4 km hr m/s m Part A Use energy to find the ball’s maximum height above the ground. Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Part B Use energy to find the ball’s speed as it passes the window on its way down. Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Part C Use energy to find the speed of impact on the ground. Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Hmax = 30 m v = 13 ms v = 24 ms Problem 10.8 A 59.0 skateboarder wants to just make it to the upper edge of a “quarter pipe,” a track that is one-quarter of a circle with a radius of 2.30 . Part A What speed does he need at the bottom? Express your answer with the appropriate units. ANSWER: Correct Problem 10.12 A 1500 car traveling at 12 suddenly runs out of gas while approaching the valley shown in the figure. The alert driver immediately puts the car in neutral so that it will roll. Part A kg m 6.71 ms kg m/s What will be the car’s speed as it coasts into the gas station on the other side of the valley? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Ups and Downs Learning Goal: To apply the law of conservation of energy to an object launched upward in the gravitational field of the earth. In the absence of nonconservative forces such as friction and air resistance, the total mechanical energy in a closed system is conserved. This is one particular case of the law of conservation of energy. In this problem, you will apply the law of conservation of energy to different objects launched from the earth. The energy transformations that take place involve the object’s kinetic energy and its gravitational potential energy . The law of conservation of energy for such cases implies that the sum of the object’s kinetic energy and potential energy does not change with time. This idea can be expressed by the equation , where “i” denotes the “initial” moment and “f” denotes the “final” moment. Since any two moments will work, the choice of the moments to consider is, technically, up to you. That choice, though, is usually suggested by the question posed in the problem. First, let us consider an object launched vertically upward with an initial speed . Neglect air resistance. Part A As the projectile goes upward, what energy changes take place? ANSWER: v = 6.8 ms K = (1/2)mv2 U = mgh Ki + Ui = Kf + Uf v Correct Part B At the top point of the flight, what can be said about the projectile’s kinetic and potential energy? ANSWER: Correct Strictly speaking, it is not the ball that possesses potential energy; rather, it is the system “Earth-ball.” Although we will often talk about “the gravitational potential energy of an elevated object,” it is useful to keep in mind that the energy, in fact, is associated with the interactions between the earth and the elevated object. Part C The potential energy of the object at the moment of launch __________. ANSWER: Both kinetic and potential energy decrease. Both kinetic and potential energy increase. Kinetic energy decreases; potential energy increases. Kinetic energy increases; potential energy decreases. Both kinetic and potential energy are at their maximum values. Both kinetic and potential energy are at their minimum values. Kinetic energy is at a maximum; potential energy is at a minimum. Kinetic energy is at a minimum; potential energy is at a maximum. Correct Usually, the zero level is chosen so as to make the relevant calculations simpler. In this case, it makes good sense to assume that at the ground level–but this is not, by any means, the only choice! Part D Using conservation of energy, find the maximum height to which the object will rise. Express your answer in terms of and the magnitude of the acceleration of gravity . ANSWER: Correct You may remember this result from kinematics. It is comforting to know that our new approach yields the same answer. Part E At what height above the ground does the projectile have a speed of ? Express your answer in terms of and the magnitude of the acceleration of gravity . ANSWER: is negative is positive is zero depends on the choice of the “zero level” of potential energy U = 0 hmax v g hmax = v2 2g h 0.5v v g h = 3 v2 8g Correct Part F What is the speed of the object at the height of ? Express your answer in terms of and . Use three significant figures in the numeric coefficient. Hint 1. How to approach the problem You are being asked for the speed at half of the maximum height. You know that at the initial height ( ), the speed is . All of the energy is kinetic energy, and so, the total energy is . At the maximum height, all of the energy is potential energy. Since the gravitational potential energy is proportional to , half of the initial kinetic energy must have been converted to potential energy when the projectile is at . Thus, the kinetic energy must be half of its original value (i.e., when ). You need to determine the speed, as a multiple of , that corresponds to such a kinetic energy. ANSWER: Correct Let us now consider objects launched at an angle. For such situations, using conservation of energy leads to a quicker solution than can be produced by kinematics. Part G A ball is launched as a projectile with initial speed at an angle above the horizontal. Using conservation of energy, find the maximum height of the ball’s flight. Express your answer in terms of , , and . Hint 1. Find the final kinetic energy Find the final kinetic energy of the ball. Here, the best choice of “final” moment is the point at which the ball reaches its maximum height, since this is the point we are interested in. u (1/2)hmax v g h = 0 v (1/2)mv2 h (1/2)hmax (1/4)mv2 h = (1/2)hmax v u = 0.707v v hmax v g Kf Express your answer in terms of , , and . Hint 1. Find the speed at the maximum height The speed of the ball at the maximum height is __________. ANSWER: ANSWER: ANSWER: Correct Part H A ball is launched with initial speed from ground level up a frictionless slope. The slope makes an angle with the horizontal. Using conservation of energy, find the maximum vertical height to which the ball will climb. Express your answer in terms of , , and . You may or may not use all of these quantities. v m 0 v v cos v sin v tan Kf = 0.5m(vcos( ))2 hmax = (vsin( ))2 2g v hmax v g ANSWER: Correct Interestingly, the answer does not depend on . The difference between this situation and the projectile case is that the ball moving up a slope has no kinetic energy at the top of its trajectory whereas the projectile launched at an angle does. Part I A ball is launched with initial speed from the ground level up a frictionless hill. The hill becomes steeper as the ball slides up; however, the ball remains in contact with the hill at all times. Using conservation of energy, find the maximum vertical height to which the ball will climb. Express your answer in terms of and . ANSWER: Correct The profile of the hill does not matter; the equation would have the same terms regardless of the steepness of the hill. Problem 10.14 A 12- -long spring is attached to the ceiling. When a 2.2 mass is hung from it, the spring stretches to a length of 17 . Part A What is the spring constant ? Express your answer to two significant figures and include the appropriate units. hmax = v2 2g v hmax v g hmax = v2 2g Ki + Ui = Kf + Uf cm kg cm k ANSWER: Correct Part B How long is the spring when a 3.0 mass is suspended from it? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Enhanced EOC: Problem 10.17 A 6.2 mass hanging from a spring scale is slowly lowered onto a vertical spring, as shown in . You may want to review ( pages 255 – 257) . For help with math skills, you may want to review: Solving Algebraic Equations = 430 k Nm kg y = 19 cm kg Part A What does the spring scale read just before the mass touches the lower spring? Express your answer to two significant figures and include the appropriate units. Hint 1. How to approach the problem Draw a picture showing the forces acting on the mass before it touches the scale. What is the net force on the mass? What is the force on the mass due to gravity? What is the force on the mass due to the scale? ANSWER: Correct Part B The scale reads 22 when the lower spring has been compressed by 2.7 . What is the value of the spring constant for the lower spring? Express your answer to two significant figures and include the appropriate units. Hint 1. How to approach the problem Draw a picture showing the forces acting on the mass. What is the net force on the mass? What is the force on the mass due to gravity? What is the force on the mass due to the scale? Use these to determine the force on the mass by the spring, taking note of the directions from your picture. How is the spring constant related to the force by the spring and the compression of the spring? Check your units. ANSWER: F = 61 N N cm k = 1400 k Nm Correct Part C At what compression length will the scale read zero? Express your answer to two significant figures and include the appropriate units. Hint 1. How to approach the problem Draw a picture showing the forces on the mass. When the scale reads zero, what is the force on the mass due to the scale? What is the gravitational force on the mass? What is the force on the mass by the spring? How is the compression length related to the force by the spring and the spring constant? Check your units. ANSWER: Correct Problem 10.18 Part A How far must you stretch a spring with = 800 to store 180 of energy? Express your answer to two significant figures and include the appropriate units. ANSWER: y = 4.2 cm k N/m J Correct Problem 10.22 A 15 runaway grocery cart runs into a spring with spring constant 230 and compresses it by 57 . Part A What was the speed of the cart just before it hit the spring? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Spring Gun A spring-loaded toy gun is used to shoot a ball straight up in the air. The ball reaches a maximum height , measured from the equilibrium position of the spring. s = 0.67 m kg N/m cm v = 2.2 ms H Part A The same ball is shot straight up a second time from the same gun, but this time the spring is compressed only half as far before firing. How far up does the ball go this time? Neglect friction. Assume that the spring is ideal and that the distance by which the spring is compressed is negligible compared to . Hint 1. Potential energy of the spring The potential energy of a spring is proportional to the square of the distance the spring is compressed. The spring was compressed half the distance, so the mass, when launched, has one quarter of the energy as in the first trial. Hint 2. Potential energy of the ball At the highest point in the ball’s trajectory, all of the spring’s potential energy has been converted into gravitational potential energy of the ball. ANSWER: Correct A Bullet Is Fired into a Wooden Block A bullet of mass is fired horizontally with speed at a wooden block of mass resting on a frictionless table. The bullet hits the block and becomes completely embedded within it. After the bullet has come to rest within the block, the block, with the bullet in it, is traveling at speed . H height = H 4 mb vi mw vf Part A Which of the following best describes this collision? Hint 1. Types of collisions An inelastic collision is a collision in which kinetic energy is not conserved. In a partially inelastic collision, kinetic energy is lost, but the objects colliding do not stick together. From this information, you can infer what completely inelastic and elastic collisions are. ANSWER: Correct Part B Which of the following quantities, if any, are conserved during this collision? Hint 1. When is kinetic energy conserved? Kinetic energy is conserved only in perfectly elastic collisions. ANSWER: perfectly elastic partially inelastic perfectly inelastic Correct Part C What is the speed of the block/bullet system after the collision? Express your answer in terms of , , and . Hint 1. Find the momentum after the collision What is the total momentum of the block/bullet system after the collision? Express your answer in terms of and other given quantities. ANSWER: Hint 2. Use conservation of momentum The momentum of the block/bullet system is conserved. Therefore, the momentum before the collision is the same as the momentum after the collision. Find a second expression for , this time expressed as the total momentum of the system before the collision. Express your answer in terms of and other given quantities. ANSWER: kinetic energy only momentum only kinetic energy and momentum neither momentum nor kinetic energy vi mw mb ptotal vf ptotal = (mw + mb)vf ptotal vi ptotal = mbvi ANSWER: Correct Problem 10.31 Ball 1, with a mass of 150 and traveling at 15.0 , collides head on with ball 2, which has a mass of 340 and is initially at rest. Part A What are the final velocities of each ball if the collision is perfectly elastic? Express your answer with the appropriate units. ANSWER: Correct Part B Express your answer with the appropriate units. ANSWER: Correct Part C vf = mb vi mb+mw g m/s g (vfx) = -5.82 1 ms (vfx) = 9.18 2 ms What are the final velocities of each ball if the collision is perfectly inelastic? Express your answer with the appropriate units. ANSWER: Correct Part D Express your answer with the appropriate units. ANSWER: Correct Enhanced EOC: Problem 10.43 A package of mass is released from rest at a warehouse loading dock and slides down the = 2.2 – high, frictionless chute to a waiting truck. Unfortunately, the truck driver went on a break without having removed the previous package, of mass , from the bottom of the chute. You may want to review ( pages 265 – 269) . For help with math skills, you may want to review: Solving Algebraic Equations (vfx) = 4.59 1 ms (vfx) = 4.59 2 ms m h m 2m Part A Suppose the packages stick together. What is their common speed after the collision? Express your answer to two significant figures and include the appropriate units. Hint 1. How to approach the problem There are two parts to this problem: the block sliding down the frictionless incline and the collision. What conservation laws are valid in each part? In terms of , what are the kinetic and potential energies of the block at the top of the incline? What is the potential energy of the same block at the bottom just before the collision? What are the kinetic energy and velocity of block just before the collision? What is conserved during the collision? What is the total momentum of the two blocks before the collision? What is the momentum of the two blocks stuck together after the collision? What is the velocity of the two blocks after the collision? ANSWER: Correct Part B Suppose the collision between the packages is perfectly elastic. To what height does the package of mass rebound? Express your answer to two significant figures and include the appropriate units. Hint 1. How to approach the problem There are three parts to this problem: the block sliding down the incline, the collision, and mass going back up the incline. What conservation laws are valid in each part? m m v = 2.2 ms m m What is an elastic collision? For an elastic collision, how are the initial and final velocities related when one of the masses is initially at rest? Using the velocity of just before the collision from Part A, what is the velocity of just after the collision in this case? What are the kinetic and potential energies of mass just after the collision? What is the kinetic energy of mass at its maximum rebound height? Using conservation of energy, what is the potential energy of mass at its maximum height? What is the maximum height? ANSWER: Correct Problem 10.35 A cannon tilted up at a 35.0 angle fires a cannon ball at 79.0 from atop a 21.0 -high fortress wall. Part A What is the ball’s impact speed on the ground below? Express your answer with the appropriate units. ANSWER: Correct Problem 10.45 A 1000 safe is 2.5 above a heavy-duty spring when the rope holding the safe breaks. The safe hits the spring and compresses it 48 . m m m m m h = 24 cm $ m/s m vf = 81.6 ms kg m cm Part A What is the spring constant of the spring? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Problem 10.49 A 100 block on a frictionless table is firmly attached to one end of a spring with = 21 . The other end of the spring is anchored to the wall. A 30 ball is thrown horizontally toward the block with a speed of 6.0 . Part A If the collision is perfectly elastic, what is the ball’s speed immediately after the collision? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Part B What is the maximum compression of the spring? Express your answer to two significant figures and include the appropriate units. ANSWER: = 2.5×105 k Nm g k N/m g m/s v = 3.2 ms Correct Part C Repeat part A for the case of a perfectly inelastic collision. Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Part D Repeat part B for the case of a perfectly inelastic collision. Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Score Summary: Your score on this assignment is 99.4%. You received 120.28 out of a possible total of 121 points. x = 0.19 m v = 1.4 ms x = 0.11 m

Assignment 8 Due: 11:59pm on Friday, April 4, 2014 You will receive no credit for items you complete after the assignment is due. Grading Policy Conceptual Question 10.3 Part A If a particle’s speed increases by a factor of 5, by what factor does its kinetic energy change? ANSWER: Correct Conceptual Question 10.11 A spring is compressed 1.5 . Part A How far must you compress a spring with twice the spring constant to store the same amount of energy? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct = 25 K2 K1 cm x = 1.1 cm Problem 10.2 The lowest point in Death Valley is below sea level. The summit of nearby Mt. Whitney has an elevation of 4420 . Part A What is the change in potential energy of an energetic 80 hiker who makes it from the floor of Death Valley to the top of Mt.Whitney? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Problem 10.3 Part A At what speed does a 1800 compact car have the same kinetic energy as a 1.80×104 truck going 21.0 ? Express your answer with the appropriate units. ANSWER: Correct Problem 10.5 A boy reaches out of a window and tosses a ball straight up with a speed of 13 . The ball is 21 above the ground as he releases it. 85m m kg U = 3.5×106 J kg kg km/hr vc = 66.4 km hr m/s m Part A Use energy to find the ball’s maximum height above the ground. Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Part B Use energy to find the ball’s speed as it passes the window on its way down. Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Part C Use energy to find the speed of impact on the ground. Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Hmax = 30 m v = 13 ms v = 24 ms Problem 10.8 A 59.0 skateboarder wants to just make it to the upper edge of a “quarter pipe,” a track that is one-quarter of a circle with a radius of 2.30 . Part A What speed does he need at the bottom? Express your answer with the appropriate units. ANSWER: Correct Problem 10.12 A 1500 car traveling at 12 suddenly runs out of gas while approaching the valley shown in the figure. The alert driver immediately puts the car in neutral so that it will roll. Part A kg m 6.71 ms kg m/s What will be the car’s speed as it coasts into the gas station on the other side of the valley? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Ups and Downs Learning Goal: To apply the law of conservation of energy to an object launched upward in the gravitational field of the earth. In the absence of nonconservative forces such as friction and air resistance, the total mechanical energy in a closed system is conserved. This is one particular case of the law of conservation of energy. In this problem, you will apply the law of conservation of energy to different objects launched from the earth. The energy transformations that take place involve the object’s kinetic energy and its gravitational potential energy . The law of conservation of energy for such cases implies that the sum of the object’s kinetic energy and potential energy does not change with time. This idea can be expressed by the equation , where “i” denotes the “initial” moment and “f” denotes the “final” moment. Since any two moments will work, the choice of the moments to consider is, technically, up to you. That choice, though, is usually suggested by the question posed in the problem. First, let us consider an object launched vertically upward with an initial speed . Neglect air resistance. Part A As the projectile goes upward, what energy changes take place? ANSWER: v = 6.8 ms K = (1/2)mv2 U = mgh Ki + Ui = Kf + Uf v Correct Part B At the top point of the flight, what can be said about the projectile’s kinetic and potential energy? ANSWER: Correct Strictly speaking, it is not the ball that possesses potential energy; rather, it is the system “Earth-ball.” Although we will often talk about “the gravitational potential energy of an elevated object,” it is useful to keep in mind that the energy, in fact, is associated with the interactions between the earth and the elevated object. Part C The potential energy of the object at the moment of launch __________. ANSWER: Both kinetic and potential energy decrease. Both kinetic and potential energy increase. Kinetic energy decreases; potential energy increases. Kinetic energy increases; potential energy decreases. Both kinetic and potential energy are at their maximum values. Both kinetic and potential energy are at their minimum values. Kinetic energy is at a maximum; potential energy is at a minimum. Kinetic energy is at a minimum; potential energy is at a maximum. Correct Usually, the zero level is chosen so as to make the relevant calculations simpler. In this case, it makes good sense to assume that at the ground level–but this is not, by any means, the only choice! Part D Using conservation of energy, find the maximum height to which the object will rise. Express your answer in terms of and the magnitude of the acceleration of gravity . ANSWER: Correct You may remember this result from kinematics. It is comforting to know that our new approach yields the same answer. Part E At what height above the ground does the projectile have a speed of ? Express your answer in terms of and the magnitude of the acceleration of gravity . ANSWER: is negative is positive is zero depends on the choice of the “zero level” of potential energy U = 0 hmax v g hmax = v2 2g h 0.5v v g h = 3 v2 8g Correct Part F What is the speed of the object at the height of ? Express your answer in terms of and . Use three significant figures in the numeric coefficient. Hint 1. How to approach the problem You are being asked for the speed at half of the maximum height. You know that at the initial height ( ), the speed is . All of the energy is kinetic energy, and so, the total energy is . At the maximum height, all of the energy is potential energy. Since the gravitational potential energy is proportional to , half of the initial kinetic energy must have been converted to potential energy when the projectile is at . Thus, the kinetic energy must be half of its original value (i.e., when ). You need to determine the speed, as a multiple of , that corresponds to such a kinetic energy. ANSWER: Correct Let us now consider objects launched at an angle. For such situations, using conservation of energy leads to a quicker solution than can be produced by kinematics. Part G A ball is launched as a projectile with initial speed at an angle above the horizontal. Using conservation of energy, find the maximum height of the ball’s flight. Express your answer in terms of , , and . Hint 1. Find the final kinetic energy Find the final kinetic energy of the ball. Here, the best choice of “final” moment is the point at which the ball reaches its maximum height, since this is the point we are interested in. u (1/2)hmax v g h = 0 v (1/2)mv2 h (1/2)hmax (1/4)mv2 h = (1/2)hmax v u = 0.707v v hmax v g Kf Express your answer in terms of , , and . Hint 1. Find the speed at the maximum height The speed of the ball at the maximum height is __________. ANSWER: ANSWER: ANSWER: Correct Part H A ball is launched with initial speed from ground level up a frictionless slope. The slope makes an angle with the horizontal. Using conservation of energy, find the maximum vertical height to which the ball will climb. Express your answer in terms of , , and . You may or may not use all of these quantities. v m 0 v v cos v sin v tan Kf = 0.5m(vcos( ))2 hmax = (vsin( ))2 2g v hmax v g ANSWER: Correct Interestingly, the answer does not depend on . The difference between this situation and the projectile case is that the ball moving up a slope has no kinetic energy at the top of its trajectory whereas the projectile launched at an angle does. Part I A ball is launched with initial speed from the ground level up a frictionless hill. The hill becomes steeper as the ball slides up; however, the ball remains in contact with the hill at all times. Using conservation of energy, find the maximum vertical height to which the ball will climb. Express your answer in terms of and . ANSWER: Correct The profile of the hill does not matter; the equation would have the same terms regardless of the steepness of the hill. Problem 10.14 A 12- -long spring is attached to the ceiling. When a 2.2 mass is hung from it, the spring stretches to a length of 17 . Part A What is the spring constant ? Express your answer to two significant figures and include the appropriate units. hmax = v2 2g v hmax v g hmax = v2 2g Ki + Ui = Kf + Uf cm kg cm k ANSWER: Correct Part B How long is the spring when a 3.0 mass is suspended from it? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Enhanced EOC: Problem 10.17 A 6.2 mass hanging from a spring scale is slowly lowered onto a vertical spring, as shown in . You may want to review ( pages 255 – 257) . For help with math skills, you may want to review: Solving Algebraic Equations = 430 k Nm kg y = 19 cm kg Part A What does the spring scale read just before the mass touches the lower spring? Express your answer to two significant figures and include the appropriate units. Hint 1. How to approach the problem Draw a picture showing the forces acting on the mass before it touches the scale. What is the net force on the mass? What is the force on the mass due to gravity? What is the force on the mass due to the scale? ANSWER: Correct Part B The scale reads 22 when the lower spring has been compressed by 2.7 . What is the value of the spring constant for the lower spring? Express your answer to two significant figures and include the appropriate units. Hint 1. How to approach the problem Draw a picture showing the forces acting on the mass. What is the net force on the mass? What is the force on the mass due to gravity? What is the force on the mass due to the scale? Use these to determine the force on the mass by the spring, taking note of the directions from your picture. How is the spring constant related to the force by the spring and the compression of the spring? Check your units. ANSWER: F = 61 N N cm k = 1400 k Nm Correct Part C At what compression length will the scale read zero? Express your answer to two significant figures and include the appropriate units. Hint 1. How to approach the problem Draw a picture showing the forces on the mass. When the scale reads zero, what is the force on the mass due to the scale? What is the gravitational force on the mass? What is the force on the mass by the spring? How is the compression length related to the force by the spring and the spring constant? Check your units. ANSWER: Correct Problem 10.18 Part A How far must you stretch a spring with = 800 to store 180 of energy? Express your answer to two significant figures and include the appropriate units. ANSWER: y = 4.2 cm k N/m J Correct Problem 10.22 A 15 runaway grocery cart runs into a spring with spring constant 230 and compresses it by 57 . Part A What was the speed of the cart just before it hit the spring? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Spring Gun A spring-loaded toy gun is used to shoot a ball straight up in the air. The ball reaches a maximum height , measured from the equilibrium position of the spring. s = 0.67 m kg N/m cm v = 2.2 ms H Part A The same ball is shot straight up a second time from the same gun, but this time the spring is compressed only half as far before firing. How far up does the ball go this time? Neglect friction. Assume that the spring is ideal and that the distance by which the spring is compressed is negligible compared to . Hint 1. Potential energy of the spring The potential energy of a spring is proportional to the square of the distance the spring is compressed. The spring was compressed half the distance, so the mass, when launched, has one quarter of the energy as in the first trial. Hint 2. Potential energy of the ball At the highest point in the ball’s trajectory, all of the spring’s potential energy has been converted into gravitational potential energy of the ball. ANSWER: Correct A Bullet Is Fired into a Wooden Block A bullet of mass is fired horizontally with speed at a wooden block of mass resting on a frictionless table. The bullet hits the block and becomes completely embedded within it. After the bullet has come to rest within the block, the block, with the bullet in it, is traveling at speed . H height = H 4 mb vi mw vf Part A Which of the following best describes this collision? Hint 1. Types of collisions An inelastic collision is a collision in which kinetic energy is not conserved. In a partially inelastic collision, kinetic energy is lost, but the objects colliding do not stick together. From this information, you can infer what completely inelastic and elastic collisions are. ANSWER: Correct Part B Which of the following quantities, if any, are conserved during this collision? Hint 1. When is kinetic energy conserved? Kinetic energy is conserved only in perfectly elastic collisions. ANSWER: perfectly elastic partially inelastic perfectly inelastic Correct Part C What is the speed of the block/bullet system after the collision? Express your answer in terms of , , and . Hint 1. Find the momentum after the collision What is the total momentum of the block/bullet system after the collision? Express your answer in terms of and other given quantities. ANSWER: Hint 2. Use conservation of momentum The momentum of the block/bullet system is conserved. Therefore, the momentum before the collision is the same as the momentum after the collision. Find a second expression for , this time expressed as the total momentum of the system before the collision. Express your answer in terms of and other given quantities. ANSWER: kinetic energy only momentum only kinetic energy and momentum neither momentum nor kinetic energy vi mw mb ptotal vf ptotal = (mw + mb)vf ptotal vi ptotal = mbvi ANSWER: Correct Problem 10.31 Ball 1, with a mass of 150 and traveling at 15.0 , collides head on with ball 2, which has a mass of 340 and is initially at rest. Part A What are the final velocities of each ball if the collision is perfectly elastic? Express your answer with the appropriate units. ANSWER: Correct Part B Express your answer with the appropriate units. ANSWER: Correct Part C vf = mb vi mb+mw g m/s g (vfx) = -5.82 1 ms (vfx) = 9.18 2 ms What are the final velocities of each ball if the collision is perfectly inelastic? Express your answer with the appropriate units. ANSWER: Correct Part D Express your answer with the appropriate units. ANSWER: Correct Enhanced EOC: Problem 10.43 A package of mass is released from rest at a warehouse loading dock and slides down the = 2.2 – high, frictionless chute to a waiting truck. Unfortunately, the truck driver went on a break without having removed the previous package, of mass , from the bottom of the chute. You may want to review ( pages 265 – 269) . For help with math skills, you may want to review: Solving Algebraic Equations (vfx) = 4.59 1 ms (vfx) = 4.59 2 ms m h m 2m Part A Suppose the packages stick together. What is their common speed after the collision? Express your answer to two significant figures and include the appropriate units. Hint 1. How to approach the problem There are two parts to this problem: the block sliding down the frictionless incline and the collision. What conservation laws are valid in each part? In terms of , what are the kinetic and potential energies of the block at the top of the incline? What is the potential energy of the same block at the bottom just before the collision? What are the kinetic energy and velocity of block just before the collision? What is conserved during the collision? What is the total momentum of the two blocks before the collision? What is the momentum of the two blocks stuck together after the collision? What is the velocity of the two blocks after the collision? ANSWER: Correct Part B Suppose the collision between the packages is perfectly elastic. To what height does the package of mass rebound? Express your answer to two significant figures and include the appropriate units. Hint 1. How to approach the problem There are three parts to this problem: the block sliding down the incline, the collision, and mass going back up the incline. What conservation laws are valid in each part? m m v = 2.2 ms m m What is an elastic collision? For an elastic collision, how are the initial and final velocities related when one of the masses is initially at rest? Using the velocity of just before the collision from Part A, what is the velocity of just after the collision in this case? What are the kinetic and potential energies of mass just after the collision? What is the kinetic energy of mass at its maximum rebound height? Using conservation of energy, what is the potential energy of mass at its maximum height? What is the maximum height? ANSWER: Correct Problem 10.35 A cannon tilted up at a 35.0 angle fires a cannon ball at 79.0 from atop a 21.0 -high fortress wall. Part A What is the ball’s impact speed on the ground below? Express your answer with the appropriate units. ANSWER: Correct Problem 10.45 A 1000 safe is 2.5 above a heavy-duty spring when the rope holding the safe breaks. The safe hits the spring and compresses it 48 . m m m m m h = 24 cm $ m/s m vf = 81.6 ms kg m cm Part A What is the spring constant of the spring? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Problem 10.49 A 100 block on a frictionless table is firmly attached to one end of a spring with = 21 . The other end of the spring is anchored to the wall. A 30 ball is thrown horizontally toward the block with a speed of 6.0 . Part A If the collision is perfectly elastic, what is the ball’s speed immediately after the collision? Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Part B What is the maximum compression of the spring? Express your answer to two significant figures and include the appropriate units. ANSWER: = 2.5×105 k Nm g k N/m g m/s v = 3.2 ms Correct Part C Repeat part A for the case of a perfectly inelastic collision. Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Part D Repeat part B for the case of a perfectly inelastic collision. Express your answer to two significant figures and include the appropriate units. ANSWER: Correct Score Summary: Your score on this assignment is 99.4%. You received 120.28 out of a possible total of 121 points. x = 0.19 m v = 1.4 ms x = 0.11 m

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Chapter 6 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 PSS 6.1 Equilibrium Problems Learning Goal: To practice Problem-Solving Strategy 6.1 for equilibrium problems. A pair of students are lifting a heavy trunk on move-in day. Using two ropes tied to a small ring at the center of the top of the trunk, they pull the trunk straight up at a constant velocity . Each rope makes an angle with respect to the vertical. The gravitational force acting on the trunk has magnitude . Find the tension in each rope. PROBLEM-SOLVING STRATEGY 6.1 Equilibrium problems MODEL: Make simplifying assumptions. VISUALIZE: Establish a coordinate system, define symbols, and identify what the problem is asking you to find. This is the process of translating words into symbols. Identify all forces acting on the object, and show them on a free-body diagram. These elements form the pictorial representation of the problem. SOLVE: The mathematical representation is based on Newton’s first law: . The vector sum of the forces is found directly from the free-body diagram. v  FG T F  = = net i F  i 0 ASSESS: Check if your result has the correct units, is reasonable, and answers the question. Model The trunk is moving at a constant velocity. This means that you can model it as a particle in dynamic equilibrium and apply the strategy above. Furthermore, you can ignore the masses of the ropes and the ring because it is reasonable to assume that their combined weight is much less than the weight of the trunk. Visualize Part A The most convenient coordinate system for this problem is one in which the y axis is vertical and the ropes both lie in the xy plane, as shown below. Identify the forces acting on the trunk, and then draw a free-body diagram of the trunk in the diagram below. The black dot represents the trunk as it is lifted by the students. Draw the vectors starting at the black dot. The location and orientation of the vectors will be graded. The length of the vectors will not be graded. ANSWER: Part B This question will be shown after you complete previous question(s). 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). A Gymnast on a Rope A gymnast of mass 70.0 hangs from a vertical rope attached to the ceiling. You can ignore the weight of the rope and assume that the rope does not stretch. Use the value for the acceleration of gravity. Part A Calculate the tension in the rope if the gymnast hangs motionless on the rope. Express your answer in newtons. You did not open hints for this part. ANSWER: Part B Calculate the tension in the rope if the gymnast climbs the rope at a constant rate. Express your answer in newtons. You did not open hints for this part. kg 9.81m/s2 T T = N T ANSWER: Part C Calculate the tension in the rope if the gymnast climbs up the rope with an upward acceleration of magnitude 1.10 . Express your answer in newtons. You did not open hints for this part. ANSWER: Part D Calculate the tension in the rope if the gymnast slides down the rope with a downward acceleration of magnitude 1.10 . Express your answer in newtons. You did not open hints for this part. ANSWER: T = N T m/s2 T = N T m/s2 T = N Applying Newton’s 2nd Law Learning Goal: To learn a systematic approach to solving Newton’s 2nd law problems using a simple example. Once you have decided to solve a problem using Newton’s 2nd law, there are steps that will lead you to a solution. One such prescription is the following: Visualize the problem and identify special cases. Isolate each body and draw the forces acting on it. Choose a coordinate system for each body. Apply Newton’s 2nd law to each body. Write equations for the constraints and other given information. Solve the resulting equations symbolically. Check that your answer has the correct dimensions and satisfies special cases. If numbers are given in the problem, plug them in and check that the answer makes sense. Think about generalizations or simplfications of the problem. As an example, we will apply this procedure to find the acceleration of a block of mass that is pulled up a frictionless plane inclined at angle with respect to the horizontal by a perfect string that passes over a perfect pulley to a block of mass that is hanging vertically. Visualize the problem and identify special cases First examine the problem by drawing a picture and visualizing the motion. Apply Newton’s 2nd law, , to each body in your mind. Don’t worry about which quantities are given. Think about the forces on each body: How are these consistent with the direction of the acceleration for that body? Can you think of any special cases that you can solve quickly now and use to test your understanding later? m2  m1 F = ma One special case in this problem is if , in which case block 1 would simply fall freely under the acceleration of gravity: . Part A Consider another special case in which the inclined plane is vertical ( ). In this case, for what value of would the acceleration of the two blocks be equal to zero? Express your answer in terms of some or all of the variables and . ANSWER: Isolate each body and draw the forces acting on it A force diagram should include only real forces that act on the body and satisfy Newton’s 3rd law. One way to check if the forces are real is to detrmine whether they are part of a Newton’s 3rd law pair, that is, whether they result from a physical interaction that also causes an opposite force on some other body, which may not be part of the problem. Do not decompose the forces into components, and do not include resultant forces that are combinations of other real forces like centripetal force or fictitious forces like the “centrifugal” force. Assign each force a symbol, but don’t start to solve the problem at this point. Part B Which of the four drawings is a correct force diagram for this problem? = 0 m2 = −g a 1 j ^  = /2 m1 m2 g m1 = ANSWER: Choose a coordinate system for each body Newton’s 2nd law, , is a vector equation. To add or subtract vectors it is often easiest to decompose each vector into components. Whereas a particular set of vector components is only valid in a particular coordinate system, the vector equality holds in any coordinate system, giving you freedom to pick a coordinate system that most simplifies the equations that result from the component equations. It’s generally best to pick a coordinate system where the acceleration of the system lies directly on one of the coordinate axes. If there is no acceleration, then pick a coordinate system with as many unknowns as possible along the coordinate axes. Vectors that lie along the axes appear in only one of the equations for each component, rather than in two equations with trigonometric prefactors. Note that it is sometimes advantageous to use different coordinate systems for each body in the problem. In this problem, you should use Cartesian coordinates and your axes should be stationary with respect to the inclined plane. Part C Given the criteria just described, what orientation of the coordinate axes would be best to use in this problem? In the answer options, “tilted” means with the x axis oriented parallel to the plane (i.e., at angle to the horizontal), and “level” means with the x axis horizontal. ANSWER: Apply Newton’s 2nd law to each body a b c d F  = ma  tilted for both block 1 and block 2 tilted for block 1 and level for block 2 level for block 1 and tilted for block 2 level for both block 1 and block 2 Part D What is , the sum of the x components of the forces acting on block 2? Take forces acting up the incline to be positive. Express your answer in terms of some or all of the variables tension , , the magnitude of the acceleration of gravity , and . You did not open hints for this part. ANSWER: Part E This question will be shown after you complete previous question(s). Part F This question will be shown after you complete previous question(s). Part G This question will be shown after you complete previous question(s). Lifting a Bucket A 6- bucket of water is being pulled straight up by a string at a constant speed. F2x T m2 g  m2a2x =F2x = kg Part A What is the tension in the rope? ANSWER: Part B This question will be shown after you complete previous question(s). Part C This question will be shown after you complete previous question(s). Friction Force on a Dancer on a Drawbridge A dancer is standing on one leg on a drawbridge that is about to open. The coefficients of static and kinetic friction between the drawbridge and the dancer’s foot are and , respectively. represents the normal force exerted on the dancer by the bridge, and represents the gravitational force exerted on the dancer, as shown in the drawing . For all the questions, we can assume that the bridge is a perfectly flat surface and lacks the curvature characteristic of most bridges. about 42 about 60 about 78 0 because the bucket has no acceleration. N N N N μs μk n F  g Part A Before the drawbridge starts to open, it is perfectly level with the ground. The dancer is standing still on one leg. What is the x component of the friction force, ? Express your answer in terms of some or all of the variables , , and/or . You did not open hints for this part. ANSWER: Part B The drawbridge then starts to rise and the dancer continues to stand on one leg. The drawbridge stops just at the point where the dancer is on the verge of slipping. What is the magnitude of the frictional force now? Express your answer in terms of some or all of the variables , , and/or . The angle should not appear in your answer. F  f n μs μk Ff = Ff n μs μk  You did not open hints for this part. ANSWER: Part C Then, because the bridge is old and poorly designed, it falls a little bit and then jerks. This causes the person to start to slide down the bridge at a constant speed. What is the magnitude of the frictional force now? Express your answer in terms of some or all of the variables , , and/or . The angle should not appear in your answer. ANSWER: Part D The bridge starts to come back down again. The dancer stops sliding. However, again because of the age and design of the bridge it never makes it all the way down; rather it stops half a meter short. This half a meter corresponds to an angle degree (see the diagram, which has the angle exaggerated). What is the force of friction now? Express your answer in terms of some or all of the variables , , and . Ff = Ff n μs μk  Ff =   1 Ff  n Fg You did not open hints for this part. ANSWER: Kinetic Friction Ranking Task Below are eight crates of different mass. The crates are attached to massless ropes, as indicated in the picture, where the ropes are marked by letters. Each crate is being pulled to the right at the same constant speed. The coefficient of kinetic friction between each crate and the surface on which it slides is the same for all eight crates. Ff = Part A Rank the ropes on the basis of the force each exerts on the crate immediately to its left. Rank from largest to smallest. To rank items as equivalent, overlap them. You did not open hints for this part. ANSWER: Pushing a Block Learning Goal: To understand kinetic and static friction. A block of mass lies on a horizontal table. The coefficient of static friction between the block and the table is . The coefficient of kinetic friction is , with . Part A m μs μk μk < μs If the block is at rest (and the only forces acting on the block are the force due to gravity and the normal force from the table), what is the magnitude of the force due to friction? You did not open hints for this part. ANSWER: Part B Suppose you want to move the block, but you want to push it with the least force possible to get it moving. With what force must you be pushing the block just before the block begins to move? Express the magnitude of in terms of some or all the variables , , and , as well as the acceleration due to gravity . You did not open hints for this part. ANSWER: Part C Suppose you push horizontally with half the force needed to just make the block move. What is the magnitude of the friction force? Express your answer in terms of some or all of the variables , , and , as well as the acceleration due to gravity . You did not open hints for this part. Ffriction = F F μs μk m g F = μs μk m g ANSWER: Part D Suppose you push horizontally with precisely enough force to make the block start to move, and you continue to apply the same amount of force even after it starts moving. Find the acceleration of the block after it begins to move. Express your answer in terms of some or all of the variables , , and , as well as the acceleration due to gravity . 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. Ffriction = a μs μk m g a =

Chapter 6 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 PSS 6.1 Equilibrium Problems Learning Goal: To practice Problem-Solving Strategy 6.1 for equilibrium problems. A pair of students are lifting a heavy trunk on move-in day. Using two ropes tied to a small ring at the center of the top of the trunk, they pull the trunk straight up at a constant velocity . Each rope makes an angle with respect to the vertical. The gravitational force acting on the trunk has magnitude . Find the tension in each rope. PROBLEM-SOLVING STRATEGY 6.1 Equilibrium problems MODEL: Make simplifying assumptions. VISUALIZE: Establish a coordinate system, define symbols, and identify what the problem is asking you to find. This is the process of translating words into symbols. Identify all forces acting on the object, and show them on a free-body diagram. These elements form the pictorial representation of the problem. SOLVE: The mathematical representation is based on Newton’s first law: . The vector sum of the forces is found directly from the free-body diagram. v  FG T F  = = net i F  i 0 ASSESS: Check if your result has the correct units, is reasonable, and answers the question. Model The trunk is moving at a constant velocity. This means that you can model it as a particle in dynamic equilibrium and apply the strategy above. Furthermore, you can ignore the masses of the ropes and the ring because it is reasonable to assume that their combined weight is much less than the weight of the trunk. Visualize Part A The most convenient coordinate system for this problem is one in which the y axis is vertical and the ropes both lie in the xy plane, as shown below. Identify the forces acting on the trunk, and then draw a free-body diagram of the trunk in the diagram below. The black dot represents the trunk as it is lifted by the students. Draw the vectors starting at the black dot. The location and orientation of the vectors will be graded. The length of the vectors will not be graded. ANSWER: Part B This question will be shown after you complete previous question(s). 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). A Gymnast on a Rope A gymnast of mass 70.0 hangs from a vertical rope attached to the ceiling. You can ignore the weight of the rope and assume that the rope does not stretch. Use the value for the acceleration of gravity. Part A Calculate the tension in the rope if the gymnast hangs motionless on the rope. Express your answer in newtons. You did not open hints for this part. ANSWER: Part B Calculate the tension in the rope if the gymnast climbs the rope at a constant rate. Express your answer in newtons. You did not open hints for this part. kg 9.81m/s2 T T = N T ANSWER: Part C Calculate the tension in the rope if the gymnast climbs up the rope with an upward acceleration of magnitude 1.10 . Express your answer in newtons. You did not open hints for this part. ANSWER: Part D Calculate the tension in the rope if the gymnast slides down the rope with a downward acceleration of magnitude 1.10 . Express your answer in newtons. You did not open hints for this part. ANSWER: T = N T m/s2 T = N T m/s2 T = N Applying Newton’s 2nd Law Learning Goal: To learn a systematic approach to solving Newton’s 2nd law problems using a simple example. Once you have decided to solve a problem using Newton’s 2nd law, there are steps that will lead you to a solution. One such prescription is the following: Visualize the problem and identify special cases. Isolate each body and draw the forces acting on it. Choose a coordinate system for each body. Apply Newton’s 2nd law to each body. Write equations for the constraints and other given information. Solve the resulting equations symbolically. Check that your answer has the correct dimensions and satisfies special cases. If numbers are given in the problem, plug them in and check that the answer makes sense. Think about generalizations or simplfications of the problem. As an example, we will apply this procedure to find the acceleration of a block of mass that is pulled up a frictionless plane inclined at angle with respect to the horizontal by a perfect string that passes over a perfect pulley to a block of mass that is hanging vertically. Visualize the problem and identify special cases First examine the problem by drawing a picture and visualizing the motion. Apply Newton’s 2nd law, , to each body in your mind. Don’t worry about which quantities are given. Think about the forces on each body: How are these consistent with the direction of the acceleration for that body? Can you think of any special cases that you can solve quickly now and use to test your understanding later? m2  m1 F = ma One special case in this problem is if , in which case block 1 would simply fall freely under the acceleration of gravity: . Part A Consider another special case in which the inclined plane is vertical ( ). In this case, for what value of would the acceleration of the two blocks be equal to zero? Express your answer in terms of some or all of the variables and . ANSWER: Isolate each body and draw the forces acting on it A force diagram should include only real forces that act on the body and satisfy Newton’s 3rd law. One way to check if the forces are real is to detrmine whether they are part of a Newton’s 3rd law pair, that is, whether they result from a physical interaction that also causes an opposite force on some other body, which may not be part of the problem. Do not decompose the forces into components, and do not include resultant forces that are combinations of other real forces like centripetal force or fictitious forces like the “centrifugal” force. Assign each force a symbol, but don’t start to solve the problem at this point. Part B Which of the four drawings is a correct force diagram for this problem? = 0 m2 = −g a 1 j ^  = /2 m1 m2 g m1 = ANSWER: Choose a coordinate system for each body Newton’s 2nd law, , is a vector equation. To add or subtract vectors it is often easiest to decompose each vector into components. Whereas a particular set of vector components is only valid in a particular coordinate system, the vector equality holds in any coordinate system, giving you freedom to pick a coordinate system that most simplifies the equations that result from the component equations. It’s generally best to pick a coordinate system where the acceleration of the system lies directly on one of the coordinate axes. If there is no acceleration, then pick a coordinate system with as many unknowns as possible along the coordinate axes. Vectors that lie along the axes appear in only one of the equations for each component, rather than in two equations with trigonometric prefactors. Note that it is sometimes advantageous to use different coordinate systems for each body in the problem. In this problem, you should use Cartesian coordinates and your axes should be stationary with respect to the inclined plane. Part C Given the criteria just described, what orientation of the coordinate axes would be best to use in this problem? In the answer options, “tilted” means with the x axis oriented parallel to the plane (i.e., at angle to the horizontal), and “level” means with the x axis horizontal. ANSWER: Apply Newton’s 2nd law to each body a b c d F  = ma  tilted for both block 1 and block 2 tilted for block 1 and level for block 2 level for block 1 and tilted for block 2 level for both block 1 and block 2 Part D What is , the sum of the x components of the forces acting on block 2? Take forces acting up the incline to be positive. Express your answer in terms of some or all of the variables tension , , the magnitude of the acceleration of gravity , and . You did not open hints for this part. ANSWER: Part E This question will be shown after you complete previous question(s). Part F This question will be shown after you complete previous question(s). Part G This question will be shown after you complete previous question(s). Lifting a Bucket A 6- bucket of water is being pulled straight up by a string at a constant speed. F2x T m2 g  m2a2x =F2x = kg Part A What is the tension in the rope? ANSWER: Part B This question will be shown after you complete previous question(s). Part C This question will be shown after you complete previous question(s). Friction Force on a Dancer on a Drawbridge A dancer is standing on one leg on a drawbridge that is about to open. The coefficients of static and kinetic friction between the drawbridge and the dancer’s foot are and , respectively. represents the normal force exerted on the dancer by the bridge, and represents the gravitational force exerted on the dancer, as shown in the drawing . For all the questions, we can assume that the bridge is a perfectly flat surface and lacks the curvature characteristic of most bridges. about 42 about 60 about 78 0 because the bucket has no acceleration. N N N N μs μk n F  g Part A Before the drawbridge starts to open, it is perfectly level with the ground. The dancer is standing still on one leg. What is the x component of the friction force, ? Express your answer in terms of some or all of the variables , , and/or . You did not open hints for this part. ANSWER: Part B The drawbridge then starts to rise and the dancer continues to stand on one leg. The drawbridge stops just at the point where the dancer is on the verge of slipping. What is the magnitude of the frictional force now? Express your answer in terms of some or all of the variables , , and/or . The angle should not appear in your answer. F  f n μs μk Ff = Ff n μs μk  You did not open hints for this part. ANSWER: Part C Then, because the bridge is old and poorly designed, it falls a little bit and then jerks. This causes the person to start to slide down the bridge at a constant speed. What is the magnitude of the frictional force now? Express your answer in terms of some or all of the variables , , and/or . The angle should not appear in your answer. ANSWER: Part D The bridge starts to come back down again. The dancer stops sliding. However, again because of the age and design of the bridge it never makes it all the way down; rather it stops half a meter short. This half a meter corresponds to an angle degree (see the diagram, which has the angle exaggerated). What is the force of friction now? Express your answer in terms of some or all of the variables , , and . Ff = Ff n μs μk  Ff =   1 Ff  n Fg You did not open hints for this part. ANSWER: Kinetic Friction Ranking Task Below are eight crates of different mass. The crates are attached to massless ropes, as indicated in the picture, where the ropes are marked by letters. Each crate is being pulled to the right at the same constant speed. The coefficient of kinetic friction between each crate and the surface on which it slides is the same for all eight crates. Ff = Part A Rank the ropes on the basis of the force each exerts on the crate immediately to its left. Rank from largest to smallest. To rank items as equivalent, overlap them. You did not open hints for this part. ANSWER: Pushing a Block Learning Goal: To understand kinetic and static friction. A block of mass lies on a horizontal table. The coefficient of static friction between the block and the table is . The coefficient of kinetic friction is , with . Part A m μs μk μk < μs If the block is at rest (and the only forces acting on the block are the force due to gravity and the normal force from the table), what is the magnitude of the force due to friction? You did not open hints for this part. ANSWER: Part B Suppose you want to move the block, but you want to push it with the least force possible to get it moving. With what force must you be pushing the block just before the block begins to move? Express the magnitude of in terms of some or all the variables , , and , as well as the acceleration due to gravity . You did not open hints for this part. ANSWER: Part C Suppose you push horizontally with half the force needed to just make the block move. What is the magnitude of the friction force? Express your answer in terms of some or all of the variables , , and , as well as the acceleration due to gravity . You did not open hints for this part. Ffriction = F F μs μk m g F = μs μk m g ANSWER: Part D Suppose you push horizontally with precisely enough force to make the block start to move, and you continue to apply the same amount of force even after it starts moving. Find the acceleration of the block after it begins to move. Express your answer in terms of some or all of the variables , , and , as well as the acceleration due to gravity . 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. Ffriction = a μs μk m g a =

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