Chapter 9 Conceptual Physics Study Guide

Transcription

1 Name : Date: Period: Chapter 9 Conceptual Physics Study Guide Multiple Choice Identify the choice that best completes the statement or answers the question. 1. In physics, work is defined as a. force times time. b. force divided by distance. c. distance divided by time. d. force divided by time. e. force times distance. 2. If you lift two loads up one story, how much work do you do compared to lifting just one load up one story? a. One quarter as much b. One half as much c. The same amount d. Twice as much e. Four times as much 3. If you lift one load up two stories, how much work do you do compared to lifting one load up only one story? a. One quarter as much b. One half as much c. The same amount d. Twice as much e. Four times as much 4. If Nellie Newton pushes an object with twice the force for twice the distance, she does a. twice the work. b. the same work. c. four times the work. d. eight times the work. 5. The unit of work is the a. watt. b. meter. c. joule. d. newton. e. second. 6. Power is defined as the a. force on an object divided by the time the force acts. b. work done times the time taken to do that work. c. work done on an object divided by the time taken to do the work. d. distance divided by the time taken to move that distance. e. force on an object times the distance the object moves. 7. The unit of power is the a. newton. b. meter. c. joule. d. second. e. watt. 8. Potential energy is the energy an object has because of its a. density. b. size. c. location. d. speed. e. temperature. 9. The amount of potential energy possessed by an elevated object is equal to a. the power used to lift it. b. the distance it is lifted. c. the force needed to lift it. d. the work done in lifting it. e. the value of the acceleration due to gravity. 10. Kinetic energy of an object is equal to a. its mass multiplied by its acceleration squared. b. one half the product of its mass times its speed squared. c. its mass multiplied by its speed. d. one half the product of its mass times its speed. e. its mass multiplied by its acceleration. 11. How much farther will a car traveling at 100 km/s skid than the same car traveling at 50 km/s? a. Half as far. b. The same distance. c. Twice as far. d. Four times as far. e. Five times as far. 12. An arrow in a bow has 70 J of potential energy. Assuming no loss of energy to heat, how much kinetic energy will it have after it has been shot? a. 0 J b. 35 J c. 50 J d. 70 J e. 140 J 13. Energy is changed from one form to another with no net loss or gain. a. Sometimes true b. Always false c. Always true 14. As a pendulum swings back and forth

2 a. at the end points of its swing, its energy is all potential. b. at the lowest part of its swing, its energy is all kinetic. c. kinetic energy is transformed into potential energy. d. potential energy is transformed into kinetic energy. e. all of the above 15. When a car s speed triples, its kinetic energy a. remains the same. b. triples. c. increases by four times. d. increases by nine times. e. none of the above 16. Rockets are launched from an airplane in the forward direction of motion. The kinetic energy of the airplane will be a. unchanged. b. increased. c. decreased. 17. A job is done slowly, and an identical job is done quickly. Both jobs require the same amount of work but different amounts of a. energy. b. power. c. both A and B d. none of the above 18. Which requires more work: lifting a 70-kg sack vertically 2 meters or lifting a 35-kg sack vertically 4 meters? a. Lifting the 70 kg sack b. Lifting the 35 kg sack c. Both require the same amount of work. 19. A ball is thrown into the air with 100 J of kinetic energy, which is transformed to gravitational potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is a. 100 J. b. more than 100 J. c. less than 100 J. d. Not enough information given. 20. An object that has kinetic energy must be a. at rest. b. falling. c. moving. d. elevated. 21. An object that has kinetic energy must have a. acceleration. b. a force applied to maintain it. c. momentum. d. none of the above 22. Which has greater kinetic energy, a car traveling at 30 km/h or a half-as-massive car traveling at 60 km/h? a. The 60 km/h car b. Both have the same kinetic energy. c. The 30 km/h car 23. A person on a roof throws one ball downward and an identical ball upward at the same speed. The ball thrown downward hits the ground with 140 J of kinetic energy. Ignoring air friction, with how much kinetic energy does the second ball hit the ground? a. less than 140 J b. 140 J c. 280 J d. more than 280 J e. none of the above 24. An object at rest may have a. energy. b. speed. c. velocity. d. momentum. e. none of the above 25. A heavy object and a light object are released from rest at the same height and time in a vacuum. As they fall, they have equal a. energies. b. weights. c. momenta. d. all of the above e. none of the above 26. If an object has kinetic energy, then it also must have a. impulse. b. force. c. momentum. d. acceleration. e. none of the above 27. If the velocity of a moving object doubles, then what else doubles? a. acceleration. b. kinetic energy. c. momentum. d. all of the above e. none of the above 28. All simple machines ideally work on the principle that a. impulse equals momentum change. b. force equals mass times acceleration. c. total momentum before a collision equals total momentum after the collision. d. work input equals work output. e. kinetic energy transforms into potential energy. 29. The ratio of output force to input force of a simple machine is called the a. fulcrum. b. efficiency. c. pivot point. d. lever arm. e. mechanical advantage.

3 30. A pulley system can a. change the direction of a force. b. multiply the force. c. increase the amount of work done. d. Both A and B e. Both B and C 31. A small economy car (low mass) and a limousine (high mass) are pushed from rest across a parking lot, equal distances with equal forces. The car that receives more kinetic energy is the a. the limousine. b. the small economy car. c. neither one they receive the same amount of kinetic energy. 32. A popular toy consists of an aligned row of identical elastic balls suspended by strings so they touch each other. When two balls on one end are elevated and released, they slam into the array of balls and two balls pop out the other side. If instead, one ball popped out with twice the speed, this would be a violation of the conservation of a. both energy and momentum. b. energy. c. momentum. 33. Consider molecules of hydrogen gas and molecules of heavier oxygen gas that have the same kinetic energy. The molecules with the greater speed are a. hydrogen. b. Both have the same speed. c. oxygen. 34. How many joules of work are done on a box when a force of 25 N pushes it 3 m? a. 1 J b. 3 J c. 8 J d. 25 J e. 75 J 35. How much power is required to do 40 J of work on an object in 5 seconds? a. 0 W b. 5 W c. 8 W d. 40 W e. 200 W 36. How much work is done on a 60-N box of books that you carry horizontally across a 6-m room? a. 0 J b. 6 J c. 10 J d. 60 J e. 360 J 37. How much work is done on a 20-N crate that you lift 2 m? a. 0 J b. 1 J c. 2 J d. 20 J e. 40 J 38. How much power is expended if you lift a 60 N crate 10 meters in 1 second? a. 0 W b. 6 W c. 10 W d. 60 W e. 600 W 39. Suppose a moving car has 3000 J of kinetic energy. If the car's speed doubles, how much kinetic energy will it then have? a J b J c J d J e. 12,000 J 40. It takes 80 J to push a large box 8 m across a floor. Assuming the push is in the same direction as the move, what is the magnitude of the force on the box? a. 8 N b. 10 N c. 80 N d. 640 N e. none of the above 41. If Kelly the skater's speed increases so he has three times the momentum, then his kinetic energy increases by a. one third times. b. three times. c. nine times. d. none of the above (KE remains the same). 42. A 60-N object moves at 1 m/s. Its kinetic energy is a. 1 J. b. 3 J. c. 60 J. d. more than 60 J. 43. Sue can easily lift a 45.0-N rock with the help of a lever. When she pushes down with 20.0 N of force, she lifts the rock 0.3 meters. How far does she move her arms to do this? a. 0.3 m b. 0.7 m c. 6.0 m d. 2.3 m e m 44. A pulley has two supporting strands. In order for it to lift a load 1 meter, the person pulling will have to pull a distance of a. m. b. m. c. 1 m. d. 2 m. e. 4 m. 45. Mechanical energy can be in the form of a. kinetic energy. b. potential energy. c. both kinetic and potential energy. d. neither kinetic nor potential energy.

4 True/False Indicate whether the statement is true or false. 46. In physics, the amount of work done on an object is the product of the force exerted on the object times the time the object moves. 47. The unit of work is called the joule. 48. The rate at which work is done is called energy. 49. The unit of power is the watt. 50. The rate at which work is done is called power. 51. The energy an object has by virtue of its location is its potential energy. 52. The energy an object has by virtue of its motion is its kinetic energy. 53. The ratio of output force to input force for a simple machine is its efficiency. 54. When we carry an object across a room, without lifting it or setting it down, we do no physical work on it. 55. More power is needed to carry a heavy suitcase slowly up a flight of stairs than to carry the suitcase quickly up the same flight of stairs. 56. Energy transforms from one form to another with no net loss or gain. 57. A pulley system can change only direction; it can't multiply forces as well. 58. In a grandfather clock, mechanical energy enables a pendulum to swing back and forth. Essay 60. Discuss how energy conservation applies to a pendulum. Where is potential energy the most? The least? Where is kinetic energy the most? The least? Where is it moving the fastest? Stopped? Problem 62. What is the work done in lifting 60 kg of blocks to a height of 20 m? 63. What is the work done in raising a 20-kg block 5 m vertically?

5 64. What amount of work is done on a chair that is pushed 9 m across a floor by a horizontal 30-N net force? 65. If possible, determine the power expended when a barbell is raised 5.0 m in 2 s. 66. A toy cart moves with a kinetic energy of 10 J. If its speed is doubled, what will its kinetic energy be? 67. In raising a 3000-N piano with a pulley system, it is noted that for every 2 m of rope pulled down, the piano rises 0.2 m. Ideally, what force is needed to lift the piano? 68. A car traveling at 50 km/h will skid 20 m when its brakes are locked. If the same car is traveling at 150 km/h, what will be its skidding distance? 69. What amount of work can a 600-W motor do in 4 minutes? 70. A couch potato might consume 7 million J of energy in a day. What is this rate of energy consumption in watts? 71. A 30-kg girl runs up the staircase to a floor 5 m higher in 8 seconds. What is her power output? 72. At what height does a 1000-kg mass have a potential energy of 1 J relative to the ground? 73. The 4.0-kg head of an ax is moving at 4.0 m/s when it strikes a log and penetrates 0.01 m into the log. What is the average force the blade exerts on the log? 74. An anvil hanging vertically from a long rope in a barn is pulled to the side and raised like a pendulum 1.60 m above its equilibrium position. It then swings to its lowermost point where the rope is cut by a sharp blade. The anvil then has a horizontal velocity with which it sails across the barn and hits the floor, 10.0 m below. How far horizontally along the floor will the anvil land?

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7 Chapter 9 Conceptual Physics Review Answer Section MULTIPLE CHOICE 1. ANS: E OBJ: 9.1 Work 2. ANS: D OBJ: 9.1 Work 3. ANS: D OBJ: 9.1 Work 4. ANS: C OBJ: 9.1 Work 5. ANS: C OBJ: 9.1 Work 6. ANS: C OBJ: 9.2 Power 7. ANS: E OBJ: 9.2 Power 8. ANS: C OBJ: 9.4 Potential Energy 9. ANS: D OBJ: 9.4 Potential Energy 10. ANS: B OBJ: 9.5 Kinetic Energy 11. ANS: D OBJ: 9.5 Kinetic Energy 12. ANS: D OBJ: 9.6 Work-Energy Theorem 13. ANS: C OBJ: 9.6 Work-Energy Theorem 14. ANS: E OBJ: 9.6 Work-Energy Theorem 15. ANS: D OBJ: 9.5 Kinetic Energy 16. ANS: C OBJ: 9.5 Kinetic Energy 17. ANS: B OBJ: 9.2 Power 18. ANS: C OBJ: 9.1 Work 19. ANS: C OBJ: 9.6 Work-Energy Theorem 20. ANS: C OBJ: 9.5 Kinetic Energy 21. ANS: C OBJ: 9.5 Kinetic Energy 22. ANS: A OBJ: 9.5 Kinetic Energy 23. ANS: B OBJ: 9.6 Work-Energy Theorem 24. ANS: A OBJ: 9.4 Potential Energy 25. ANS: E OBJ: 9.3 Mechanical Energy 26. ANS: C OBJ: 9.5 Kinetic Energy 27. ANS: C OBJ: 9.5 Kinetic Energy 28. ANS: D OBJ: 9.7 Conservation of Energy 29. ANS: E OBJ: 9.7 Conservation of Energy 30. ANS: D OBJ: 9.7 Conservation of Energy 31. ANS: C OBJ: 9.5 Kinetic Energy 32. ANS: B OBJ: 9.6 Work-Energy Theorem 33. ANS: A OBJ: 9.5 Kinetic Energy 34. ANS: E OBJ: 9.1 Work 35. ANS: C OBJ: 9.2 Power 36. ANS: A OBJ: 9.1 Work 37. ANS: E OBJ: 9.1 Work 38. ANS: E OBJ: 9.2 Power 39. ANS: E OBJ: 9.5 Kinetic Energy 40. ANS: B OBJ: 9.1 Work 41. ANS: C OBJ: 9.5 Kinetic Energy

8 42. ANS: B OBJ: 9.5 Kinetic Energy 43. ANS: B OBJ: 9.7 Conservation of Energy 44. ANS: D OBJ: 9.7 Conservation of Energy 45. ANS: C OBJ: 9.3 Mechanical Energy TRUE/FALSE 46. ANS: F OBJ: 9.1 Work 47. ANS: T OBJ: 9.1 Work 48. ANS: F OBJ: 9.2 Power 49. ANS: T OBJ: 9.2 Power 50. ANS: T OBJ: 9.2 Power 51. ANS: T OBJ: 9.4 Potential Energy 52. ANS: T OBJ: 9.5 Kinetic Energy 53. ANS: F OBJ: 9.7 Conservation of Energy 54. ANS: T OBJ: 9.1 Work 55. ANS: F OBJ: 9.2 Power 56. ANS: T OBJ: 9.6 Work-Energy Theorem 57. ANS: F OBJ: 9.7 Conservation of Energy 58. ANS: T OBJ: 9.3 Mechanical Energy ESSAY 59. ANS: The work you do when lifting something may be stored as gravitational potential energy. Then the force times the distance is equal to the weight times the height. If the lifted object is released, this energy transforms to motion energy (or kinetic energy). The kinetic energy as it returns to its starting point equals the gravitational potential energy at its highest point, which in turn equals the work done on it in the first place. OBJ: 9.6 Work-Energy Theorem 60. ANS: Net energy is never created or destroyed. It can change from one form to another form. A swinging pendulum has the most gravitational potential energy at the top of its swing. At that point it has no kinetic energy. At the bottom of its swing its potential energy is at a minimum, or zero relative to that lowermost point, and its kinetic energy is at a maximum. Halfway down, it has half kinetic and half potential energy. Everywhere along the swing the sum of the kinetic and potential energies is the same. When air resistance and friction are taken into account, energy is transferred from the pendulum to the surroundings in the form of heat. OBJ: 9.6 Work-Energy Theorem PROBLEM 62. ANS: 12,000 J OBJ: 9.1 Work 63. ANS:

9 1000 J OBJ: 9.1 Work 64. ANS: 270 J OBJ: 9.1 Work 65. ANS: dependent on the mass of the barbell OBJ: 9.2 Power 66. ANS: 40 J OBJ: 9.5 Kinetic Energy 67. ANS: 300 N OBJ: 9.7 Conservation of Energy 68. ANS: 180 m OBJ: 9.5 Kinetic Energy 69. ANS: 144,000 J OBJ: 9.2 Power 70. ANS: 81 W OBJ: 9.2 Power 71. ANS: 188 W OBJ: 9.2 Power 72. ANS: 0.00 m OBJ: 9.4 Potential Energy 73. ANS: 3200 N OBJ: 9.5 Kinetic Energy 74. ANS: 8.0 m OBJ: 9.6 Work-Energy Theorem