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5, Chapter Energy CHAPTER 5 5.1 Work 1. The unit of work, joule, is dimensionally the same as: a. newton/second. b. newton/kilogram. c. newton-second. d. newton-meter. 2. Rupel pushes a box 5.00 m by applying a 25.0-N horizontal force. What work does she do? a. 10.0 J b. 25.0 J c. 125 J d. 550 J 3. A worker pushes a sled with a force of 40 N over a level distance of 6.0 m. If a frictional force of 24 N acts on the wheelbarrow in a direction opposite to that of the worker, what net work is done on the wheelbarrow? a. 240 J b. 216 J c. 144 J d. 96 J 4. A horizontal force of 100 N is applied to move a 45-kg cart across a 9.0-m level surface. What work is done by the 100-N force? a. 405 J b. 500 J c. 900 J d. 4 500 J 5. I use a rope 2.00 m long to swing a 10.0-kg weight around my head. The tension in the rope is 20.0 N. In half a revolution how much work is done by the rope on the weight? a. 40.0 J b. 126 J c. 251 J d. 0 56 Chapter 5, Energy 6. The work done by static friction can be: a. positive. b. negative. c. zero. d. Any of the a bove. 7. A satellite is held in orbit by a 2 000-N gravitational force. Each time the satellite completes an orbit of circumference 80 000 km, the work done on it by gravity is: a. 1.6 x 10 8 J. b. 1.6 x 1011 J. c. 6.4 x 1011 J. d. 0. 5.2 Kinetic energy and the Work-Energy Theorem 8. Which of the following is an example of a nonconservative force? a. gravity b. magnetism c. friction d. Both choices A and B are valid. 9. Which of the following is that form of energy associated with an objects motion? a. potential b. thermal c. bio-chemical d. kinetic 10. Which of the following is that form of energy associated with an objects location in a conservative force field? a. potential b. thermal c. bio-chemical d. kinetic 11. What is the kinetic energy of a 0.135-kg baseball thrown at 40.0 m/s (90.0 mph)? a. 54.0 J b. 87.0 J c. 108 J d. 216 J 57 Chapter 5, Energy 12. A horizontal force of 200 N is applied to a 55-kg cart across a 10 -m level surface. If the cart accelerates at 2.0 m/s2, then what is the work done by the force of friction as it acts to retard the motion of the cart? a. -1 100 J b. -900 J c. -800 J d. -700 J 13. A golf ball hits a wall and bounces back at 3/4 the original speed. What part of the original kinetic energy of the ball did it lose in the collision? a. 1/4 b. 3/8 c. 7/16 d. 9/16 14. If both mass and velocity of a ball are tripled, the kinetic energy is increased by a factor of: a. 3. b. 6. c. 9. d. 27. 15. A 1 200 -kg automobile moving at 25 m/s has the brakes applied with a deceleration of 8.0 m/s2. How far does the car travel before it stops? a. 39 m b. 47 m c. 55 m d. 63 m 16. If during a given physical process the only force acting on an object is friction, which of the following must be assumed in regard to the objects kinetic energy? a. decreases b. increases c. remains constant d. cannot tell from the information given 5.3 Gravitational Potential Energy 17. A very light cart holding a 300-N box is moved at constant velocity across a 15-m level surface. What is the net work done in the process? a. zero b. 1/20 J c. 20 J 58 Chapter 5, Energy d. 2 000 J 18. A 7.00-kg bowling ball falls from a 2.00-m shelf. Just before hitting the floor, what will be its kinetic energy? (g = 9.80 m/s 2 and assume air resistance is negligible) a. 14.0 J b. 19.6 J c. 29.4 J d. 137 J 19. A rock is thrown straight up with an initial velocity of 15.0 m/s. Ignore energy lost to air friction. How high will the rock rise? a. 1.53 m b. 22.9 m c. 6.50 m d. 11.5 m 20. What is the minimum amount of energy required for an 80 -kg climber carrying a 20-kg pack to climb Mt. Everest, 8 850 m high? a. 8.67 MJ b. 4.16 MJ c. 2.47 MJ d. 1.00 MJ 21. A professional skier reaches a speed of 56 m/s on a 30 ski slope. Ignoring friction, what was the minimum distance along the slope the skier would have had to travel, starting from rest? a. 110 m b. 160 m c. 320 m d. 640 m 22. As an object is lowered into a deep hole in the surface of the earth, which of the following must be assumed in regard to its potential energy? a. increase b. decrease c. remain constant d. cannot tell from the information given 23. When an object is dropped from a tower, what is the effect of the air resistance as it falls? a. does positive work b. increases the objects kinetic energy c. increases the objects potential energy d. None of the above choices are valid. 59 Chapter 5, Energy 60 Chapter 5, Energy 24. Samantha pushes a 50-N crate up a ramp 25.0 m in length and inclined at 10 with the horizontal. What potential energy change does the crate experience? a. 13 J b. 55 J c. 120 J d. 220 J 25. A 15.0-kg crate, initially at rest, slides down a ramp 2.0 m long and inclined at an angle of 20 with the horizontal. If there is no friction between ramp surface and crate, what is the kinetic energy of the crate at the bottom of the ramp? (g = 9.8 m/s 2) a. 220 J b. 690 J c. 10 J d. 100 J 26. A 10.0-kg box starts at rest and slides 3.5 m down a ramp inclined at an angle of 10 with the horizontal. If there is no friction between the ramp surface and crate, what is the velocity of the crate a t the bottom of the ramp? (g = 9.8 m/s 2) a. 6.1 m/s b. 3.5 m/s c. 10.7 m/s d. 8.3 m/s 27. A baseball catcher puts on an exhibition by catching a 0.15-kg ball dropped from a helicopter at a height of 101 m. What is the speed of the ball just before it hits the catchers glove 1.0 m above the ground? (g = 9.8 m/s 2 and ignore air resistance) a. 44 m/s b. 38 m/s c. 31 m/s d. 22 m/s 28. A simple pendulum, 1.00 m in length, is released from rest when the support string is at an angle of 35.0 from the vertical. What is the speed of the suspended mass at the bottom of the swing? (g = 9.80 m/s 2 and ignore air resistance) a. 0.67 m/s b. 0.94 m/s c. 1.33 m/s d. 1.88 m/s 61 Chapter 5, Energy 29. A simple pendulum, 2.0 m in length, is released with a push when the support string is at an angle of 25 from the vertical. If the initial speed of the suspended mass is 1.2 m/s when at the release point, what is its speed at the bottom of the swing? (g = 9.8 m/s 2) a. 2.3 m/s b. 2.6 m/s c. 2.0 m/s d. 0.5 m/s 30. A simple pendulum, 2.0 m in length, is released by a push when the support string is at an angle of 25 from the vertical. If the initial speed of the suspended mass is 1.2 m/s when at the release point, to what maximum angle will it move in the second half of its swing? a. 37 b. 30 c. 27 d. 21 31. A hill is 100 m long and makes an angle of 12 with the horizontal. As a 50-kg jogger runs up the hill, how much work does gravity do on the jogger? a. 49 000 J b. 10 000 J c. 10 000 J d. zero 32. A 2.00-kg ball has zero kinetic and potential energy. Ernie drops the ball into a 10.0-m-deep well. Just before the ball hits the bottom, the sum of its kinetic and potential energy is: a. zero. b. 196 J. c. 196 J. d. 392 J. 33. A 2.00-kg ball has zero potential and kinetic energy. Maria drops the ball into a 10.0-m-deep well. After the ball comes to a stop in the mud, the sum of its potential and kinetic energy is: a. zero. b. 196 J. c. 196 J. d. 392 J. 62 Chapter 5, Energy 34. Two blocks are released from the top of a building. One falls straight down while the other slides down a smooth ramp. If all friction is ignored, which one is moving faster when it reaches the bottom? a. The block that went straight down. b. The block that went down the ramp. c. They both will have the same speed. d. Insufficient information to work the problem. 35. Old Faithful geyser in Yellowstone Park shoots water hourly to a height of 40 m. With what velocity does the water leave the ground? a. 7.0 m/s b. 14 m/s c. 20 m/s d. 28 m/s 36. An 80 000 -kg airliner is flying at 900 km/h at a height of 10.0 km. What is its total energy (kinetic + potential) if the total was 0 when the airliner was at rest on the ground? a. 250 MJ b. 478 MJ c. 773 MJ d. 10 300 MJ 37. A pole vaulter clears 6.00 m. With what speed does he strike the mat in the landing area? a. 2.70 m/s b. 5.40 m/s c. 10.8 m/s d. 21.6 m/s 38. A baseball outfielder throws a baseball of mass 0.15 kg at a speed of 40 m/s and initial angle of 30 . What is the kinetic energy of the baseball at the highest point of the trajectory? Ignore air friction. a. zero b. 30 J c. 90 J d. 120 J 39. A bobsled makes a run down an ice track starting at 150 m vertical distance up the hill. If there is no friction, what is the velocity at the bottom of the hill? a. 27 m/s b. 36 m/s c. 45 m/s d. 54 m/s 63 Chapter 5, Energy 5.4 Spring Potential Energy 40. A 2 000 -kg ore car rolls 50.0 m down a frictionless 10.0 incline. If there is a horizontal spring at the end of the incline, what spring constant is required to stop the ore car in a distance of 1.00 m? a. 340 kN/m b. 681 kN/m c. 980 kN/m d. 1 960 kN/m 41. An amount of work equal to 1.5 J is required to compress the spring in a spring-gun. What is the launch speed of a 15 -g marble? a. 14 m/s b. 15 m/s c. 18 m/s d. 21 m/s 42. The SI units for k, the spring constant, are equivalent to: a. J. b. J / N. c. kg / s2. d. None of the above. 43. By how much is the energy stored a in Hookes law spring increased when its stretch is increased from 8.00 cm to 16.0 cm? a. 100% b. 200% c. 300 % d. The correct answer is not given. 44. A Hookes law spring is compressed 12.0 cm from equilibrium and the potential energy stored is 72.0 J. What is the spring constant in this case? a. 10 000 N/m b. 5 000 N/m c. 1 200 N/m d. No answer is correct. 64 Chapter 5, Energy 45. A Hookes law spring is compressed 12.0 cm from equilibrium, and the potential energy stored is 72.0 J. What compression (as measured from equilibrium) would result in 100 J being stored in this case? a. 16.7 cm b. 14.1 cm c. 13.6 cm d. No answer is correct. 46. A Hookes law spring is mounted horizontally over a frictionless surface. The spring is then compressed a distance d and is used to launch a mass m along the frictionless surface. What compression of the spring would result in the mass attaining double the kinetic energy received in the above situation? a. 1.41 d b. 1.73 d c. 2.00 d d. 4.00 d 47. A Hookes law spring is mounted horizontally over a frictionless surface. The spring is then compressed a distance d a nd is used to launch a mass m along the frictionless surface. What compression of the spring would result in the mass attaining double the speed received in the above situation? a. 1.41 d b. 1.73 d c. 2.00 d d. 4.00 d 5.5 Systems and Energy Conserv ation 48. A 50-N crate is pulled up a 5 -m inclined plane by a worker at constant velocity. If the plane is inclined at an angle of 37 to the horizontal and there exists a constant frictional force of 10 N between the crate and the surface, what is the force applied by the worker? a. zero b. 20 N c. 30 N d. 40 N 49. Adisa pulls a 40-N crate up a 5.0 -m long inclined plane at a constant velocity. If the plane is inclined at an angle of 37 to the horizontal and there is a constant force of friction of 10 N between the crate and the surface, what is the net change in potential energy of the crate? a. 120 J b. 120 J c. 200 J d. 200 J 65 Chapter 5, Energy 66 Chapter 5, Energy 50. A 20-N crate starting at rest slides down a rough 5.0-m long ramp, inclined at 25 with the horizontal. 20 J of energy is lost to friction. What will be the speed of the crate at the bottom of the incline? a. 0.98 m/s b. 1.9 m/s c. 3.2 m/s d. 4.7 m/s 51. Preston pushes a wheelbarrow weighing 500 N to the top of a 50.0-m ramp, inclined at 20.0 with the horizontal, and leaves it. Tamara accidentally bumps the wheelbarrow. It slides back down the ramp, during which an 80.0-N frictional force acts on it over the 50.0 m. What is the wheelbarrows kinetic energy at the bottom at of the ramp? (g = 9.8 m/s 2) a. 4 550 J b. 6 55 0 J c. 8 150 J d. 13 100 J 52. A pile driver drives a post into the ground. The mass of the pile driver is 2 500 kg and it is dropped through a height of 8.0 m on each stroke. If the resisting force of the ground is 4.0 106 N, how far is the post driven in on each stroke? a. 4.9 cm b. 9.8 cm c. 16 cm d. 49 cm 53. A baseball catcher puts on an exhibition by catching a 0.150-kg ball dropped from a helicopter at a height of 100 m above the catcher. If the catcher "gives" with the ball for a distance of 0.750 m while catching it, what average force is exerted on the mitt by the ball? (g = 9.80 m/s 2) a. 78 N b. 119 N c. 197 N d. 392 N 54. A girl and her bicycle have a total mass of 40.0 kg. At the top of the hill her speed is 5.0 m/s, and her speed doubles as she rides down the hill. The hill is 10.0 m high and 100 m long. How much kinetic energy and potential energy is lost to friction? a. 2 420 J b. 1 500 J c. 2 000 J d. 3 920 J 67 Chapter 5, Energy 55. A girl and her bicycle have a total mass of 40 kg. At the top of the hill her speed is 5.0 m/s. The hill is 10 m high and 100 m long. If the force of friction as she rides down the hill is 20 N, what is her speed at the bottom? a. 5.0 m/s b. 10 m/s c. 11 m/s d. She stops before she reaches the bottom. 56. I drop a 60 -g golf ball from 2.0 m high. It rebounds to 1.5 m. How much energy is lost? a. 0.29 J b. 0.50 J c. 0.88 J d. 1.0 J 57. A parachutist of mass 50.0 kg jumps out of an airplane at a height of 1 000 m. The parachute deploys, and she lands on the ground with a speed of 5.0 m/s. How much energy was lost to air friction during this jump? a. 49 400 J b. 98 700 J c. 198 000 J d. 489 000 J 58. A Hookes law spring is compressed a distance d and is used to launch a mass m vertically to a height h above its starting position. Under the same compression d, the spring is now used to launch a mass of 2m. How high does this second mass rise? a. h b. h/2 c. h/1.41 d. h/4 59. A Hookes law spring is compressed a distance d and is used to launch a mass m vertically to a height h above its starting position. Under double the compression, the spring is now used to launch the mass. How high does the mass now rise above its starting position? a. 2 h b. 1.41 h c. 3 h d. 4 h 68 Chapter 5, Energy 60. A Hookes law spring is compressed a distance d and is used to launch a particle of mass m vertically to a height h above its starting position. Under double the compression, the spring is now used to launch a particle of mass 2 m. How high does the second mass rise above its starting position? a. h b. 2 h c. 3 h d. 4 h 5.6 Power 61. The quantity of work equal to one joule is also equivalent to which of the following? a. watt b. watt /s c. watt s d. watt /s2 62. The rate at which work is done is equivalent to which of the following? a. increase in potential energy b. thermal energy c. potential energy d. power 63. The unit of power, watt, is dimensionally the same as: a. joule-second. b. joule/second. c. joule-meter. d. joule/meter. 64. A 60-kg woman runs up a flight of stairs having a rise of 4.0 m in a time of 4.2 s. What average power did she supply? a. 380 W b. 560 W c. 620 W d. 670 W 65. An automobile delivers 30.0 hp to its wheels when moving at a constant speed of 22.0 m/s. What is the resistance force on the automobile at this speed? (1 hp = 746 watts) a. 18 600 N b. 410 000 N c. 1 020 N d. 848 N 69 Chapter 5, Energy 66. Yuri, a Russian weightlifter, is able to lift 250 kg 2.00 m in 2.00 s. What is his power output? a. 500 W b. 2.45 kW c. 4.90 kW d. 9.80 kW 67. A jet engine develops 1.0 105 N of thrust in moving an airplane forward at a speed of 900 km/h. What is the power developed by the engine? a. 500 kW b. 10 MW c. 25 MW d. 50 MW 68. A speed boat requires 80 kW to move at a constant speed of 15 m/s. What is the resistive force of the water at this speed? a. 2 700 N b. 5 300 N c. 6 500 N d. 7 700 N 69. Water flows over a section of Niagara Falls at a rate of 1.20 106 kg/s and falls 50.0 m. What is the power dissipated by the waterfall? a. 588 MW b. 294 MW c. 147 MW d. 60.0 MW 70. A 1 000 -kg sports car accelerates from zero to 25 m/s in 7.5 s. What is the average power delivered by the automobile engine? a. 20.8 kW b. 30.3 kW c. 41.7 kW d. 52.4 kW 71. A force of 5.0 N is applied to a 20 -kg mass on a horizontal frictionless surface. As the speed of the mass increases at a constant acceleration, the power delivered to it by the force: a. remains the same. b. increases. c. decreases. d. doubles every 4.0 seconds. 70 Chapter 5, Energy 71 Chapter 5, Energy 72. A 100 -W light bulb is left on for 1 0.0 hours. Over this period of time, how much energy was used by the bulb? a. 1 000 J b. 3 600 J c. 3 600 000 J d. 1.34 hp 73. A 200 -hp engine can deliver, in SI units, an average power of ________. (1 hp = 746 W) a. 200 W b. 74 600 W c. 149 000 W d. 298 000 W 5.7 Work Done by a Varying Force 74. The area under the force vs. displacement curve represents: a. area. b. force. c. work. d. coefficient of static friction. 75. A force of 100 N is applied to a 50-kg mass in the direction of motion for a distance of 6.0 m and then the force is increased to 150 N for the next 4.0 m. For the 10 m of travel, how much work is done by the varying force? a. 1 200 J b. 1 500 J c. 2 400 J d. 1 500 J 76. The net force acting on a 6.0-kg object is given by Fx = (10 x) N, where Fx is in newtons and x is in meters. How much work is done on the object as it moves from x = 0 to x = 10 m? a. 100 J b. 75 J c. 50 J d. 25 J 77. The net force acting on a 12.6-kg object is given by Fx = (20 x) N, where Fx is in newtons and x is in meters. How much work is done on the object as it moves from x = 0 to x = 10 m? a. 300 J b. 200 J c. 150 J d. 100 J 72 Chapter 5, Energy CHAPTER 5 - ANSWERS # 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. Ans D C D C D D D C D A C B C D A D A D D A C B D D D B A D A B C A C C D D C C D Difficulty 1 1 2 1 2 2 2 1 1 1 1 2 2 1 2 1 1 1 2 2 2 1 1 1 2 2 2 2 3 3 1 1 2 1 2 2 2 2 2 # 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76 77. Ans A A C C A B A C D A D A A C A C A D B D B C D B B C B C B A C B C C C A C C Difficulty 2 2 2 2 2 3 2 3 2 2 2 2 2 2 2 2 2 2 2 2 2 1 1 1 2 2 2 2 2 3 2 2 2 1 1 2 3 3 73 ... View Full Document