Work Power And Energy TEACHER ANSWER KEY 1 Power And Energy TEACHER ANSWER KEY March 09, 2004 1 1. A...

Work Power And Energy TEACHER ANSWER KEY March 09, 2004

1 1. A spring has a spring constant of 120 newtons/meter. How much potential energy is stored in the spring as it is stretched 0.20 meter?

1. 2.4 J 3. 12 J

2. 4.8 J 4. 24 J

No Explanation Available.

1 2. A 10.-newton force is required to move a 3.0-kilogram box at constant speed. How much power is required to move the box 8.0 meters in 2.0 seconds?

1. 40. W 3. 15 W

2. 20. W 4. 12 W


2 3. Spring A has a spring constant of 140 newtons per meter, and spring B has a spring constant of 280 newtons per meter. Both springs are stretched the same distance. Compared to the potential energy stored in spring A, the potential energy stored in spring B is

1. the same 3. half as great

2. twice as great 4. four times as great


1 4. A cart of mass m traveling at speed v has kinetic energy KE. If the mass of the cart is doubled and its speed is halved, the kinetic energy of the cart will be

1. half as great 3. one-fourth as great


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4 5. A 4.0 x 103 watt motor applies a force of 8.0 X 102 newtons to move a boat at constant speed. How far does the boat move in 16 seconds?

1. 3.2 m 3. 32 m

2. 5.0 m 4. 80 m


4 6. When a spring is stretched 0.200 meters from its equilibrium position, it posseses a potential energy of 10.0 joules. What is the spring constant for this spring?

1. 100 N/m 3. 250 N/m

2. 125 N/m 4. 500 N/m


1 7. A force applied to a block, causing it to accelerate along a horizontal, frictionless surface. The energy gained by the block is equal to the

1. work done on the block 3. impulse applied to the block

2. power applied to the block 4. momentum given to the block


2 8. A student pulls a block 3.0 meters along a horizontal surface at constant velocity.The diagram shows the components of the force exerted on the block by the student. How much work is done against friction?



1. 18 J 3. 30. J

2. 24 J 4. 42 J


3 9. In the diagram, an ideal pendulum released from point A swings freely through point B. Compared to the pendulum's kinetic energy at A, its potential energy at B is

1. half as great 3. the same



3 10. A 5.0 × 102-newton girl takes 10. seconds to run up two flights of stairs to a landing, a total of 5.0 meters vertically above her starting point. What power does the girl develop during her run?

1. 25 W 3. 250 W

2. 50. W 4. 2,500 W



3 11. A student rides a bicycle up to a 30.' hill at a constant speed of 6.00 meters per second. The combined mass of the student and the bicycle is 70.0 kilograms. What is the kinetic energy of the student-bicycle system during this ride?

1. 210. J 3. 1,260 J

2. 420. J 4. 2,520 J


3 12. A net force of 5.0 newtons moves a 2.0-kilogram object a distance of 3.0 meters in 3.0 seconds. How much work is done on the object?

1. 1.0 J 3. 15 J

2. 10. J 4. 30. J


4 13. Which graph represents the relationship between the elongation of a spring whose elastic limit has not been reached and the force applied to it?




4 14. Base your answer on the diagram which represents a frictionless track. A 10-kilogram block starts from rest at point A and slides along the track. As the block moves from point A to point B, the total amount of gravitational potential energy changed to kinetic energy is approximately

1. 5 J 3. 50 J

2. 20 J 4. 500 J


2 15. Base your answer on the diagram which represents a frictionless track. A 10-kilogram block starts from rest at point A and slides along the track. What is the approximate speed of the block at point B?



1. 1 m/s 3. 50 m/s

2. 10 m/s 4. 100 m/s


2 16. Base your answer on the diagram which represents a frictionless track. A 10-kilogram block starts from rest at point A and slides along the track. What is the approximate potential energy of the block at point C?

1. 20 J 3. 300 J

2. 200 J 4. 500 J


3 17. Two vacationers walk out on a horizontal pier as shown in the accompanying diagram. As they approach the end of the pier, their gravitational potential energy will

1. decrease 3. remain the same

2. increase



1 18. The accompanying graph represents the elongation of a spring as a function of the applied force. How much work must be done to stretch the spring 0.40 meter?

1. 4.8 J 3. 9.8 J

2. 6.0 J 4. 24 J

1



19. In the accompanying diagram, a 20.0-newton force is used to push a 2.00-kilogram cart a distance of 5.00 meters. The work done on the cart is

1. 100. J 3. 150. J

2. 200. J 4. 40.0 J

4 20. Which combination of units can be used to express work?

3 21. A 2000-watt motor working at full capacity can vertically life a 400-newton weight at a constant speed of



1. 2 X 103 m/s 3. 5 m/s

2. 50 m/s 4. 0.2 m/s

2 22. The accompanying diagram shows block A, having mass 2m and speed v, and block B having mass m and speed 2v. Compared to the kinetic energy of block A, the kinetic energy of block B is

1. the same 3. one-half as great


1 23. The unstretched spring in the diagram has a length of 0.40 meter and spring constant k. A weight is hung from the spring, causing it to stretch to a length of



0.60 meter.

1. 0.020 X k 3. 0.18 X k

2. 0.080 X k 4. 2.0 X k

3 24. A spring has a spring constant of 25 newtons per meter. The minimum force required to stretch the spring 0.25 meter from its equilibrium position is approximately

1. 1.0 X 10-4 N 3. 6.3 N

2. 0.78 N 4. 1.0 X 102 N



1 25. If the time required for a student to swim 500 meters is doubled, the power developed by the student will be

1. halved 3. quartered

2. doubled 4. quadrupled

3 26. In the diagram , an average force of 20. newtons is used to pull back the string of a bow 0.60 meter.



1. 3.4 J 3. 12 J

2. 6.0 J 4. 33 J

3 27. Base your answer to the following question on the diagram. A planet, P, moves around the Sun, S, in an elliptical orbit. The amount of time required for the planet to travel from point A to point B is equal to the amount of time required to travel from point C to point D. As the planet moves from point B to point C, how do its kinetic energy and potential energy change?



1. Its kinetic energy decreases, and its potential energy decreases.

3. Its kinetic energy increases, and its potential energy decreases.

2. Its kinetic energy decreases, and its potential energy increases.

4. Its kinetic energy increases, and its potential energy increases.

3 28. A student pulls a box across a horizontal floor at a constant speed of 4.0 meters per second by exerting a constant horizontal force of 45 newtons. Approximately how much work does the student do against friction in moving the box 5.5 meters across the floor?

1. 45 J 3. 250 J

2. 180 J 4. 740 J



2 29. A 45-kilogram bicyclist climbs a hill at a constant speed of 2.5 meters per second by applying an average force of 85 newtons. Approximately how much power does the bicyclist develop?

1. 110 W 3. 1100 W

2. 210 W 4. 1400 W

4 30. Which action would require no work to be done on an object?

1. lifting the object from the floor to the ceiling

3. decreasing the speed of the object until it comes to rest

2. pushing the object along a horizontal floor against a frictional

4. holding the object stationary above the ground



force

1 31. The diagram shows a 1.5-kilogram kitten jumping from the top of a 1.80-meter-high refrigerator to a 0.90-meter-high counter.

1. half as great 3. one-fourth as great




2 32. A cart of mass M on a frictionless track starts from rest at the top of a hill having height h1, as shown in the diagram. What is the kinetic energy of the cart when it reaches the top of the next hill, having height h2?

1. Mgh1 3. Mg(h2 - h3)

2. Mg(h1 - h2) 4. 0


4 33. How much work is done on a downhill skier by an average braking force of 9.8 x 102 newtons to stop her in a distance of 10. meters?

1. 1.0 x 101 J 3. 1.0 X 103J

2. 9.8 x 102J 4. 9.8 x 103 J




3 34. Which variable expression is paired vath a corresponding unit?


4 35. The accompanying diagram shows three positions, A, B, and C, in the swing of a pendulum, released from rest at point A. [Neglect friction.] Which statement is true about this swinging pendulum?

1. The potential energy at A equals the kinetic energy at C.

3. The potential energy at B equals the potential energy at C.

2. The speed of the pendulum at A equals the speed of the pendulum at B.

4. The potential energy at A equals the kinetic energy at B.



1 36. A 500.-newton girl lifts a 10.-newton box vertically upward a distance of 0.50 meter. The work done on the box is

3 37. Which graph best represents the relationship between the kinetic energy of a moving object and its velocity?



4 38. How much work is done on a downhill skier by an average braking force of 9.8 X 102 newtons to stop her in a distance of 10. meters?

1 39. A spring has a spring constant of 120 newtons per meter. How much potential energy is stored in the spring as it is stretched 0.20 meter?

4



40. The accompanying graph shows the relationship between the elongation of a spring and the force applied to the spring causing it to stretch. What is the spring constant for this spring?

1. 0.020 N/m 3. 25 N/m

2. 2.0 N/m 4. 50. N/m

1 41. A 10.-newton force is required to move a 3.0-kilogram box at constant speed. How much power is required to move the box 8.0 meters in 2.0 seconds?

1. 40. W 3. 15 W

2. 20. W 4. 12 W

2 42. A 0.10-kilogram ball dropped vertically from a height of 1.00 meter above the floor bounces back to a height of 0.80 meter. The mechanical energy lost



by the ball as it bounces is

2 43. An object moving at a constant speed of 25 meters per second possesses 450 joules of kinetic energy. What is the object's mass?

1. 0.72 kg 3. 18 kg

2. 1.4 kg 4. 36 kg

4



44. The accompanying diagram shows a moving, 5.00-kilogram cart at the foot of a hill 10.0 meters high. For the cart to reach the top of the hill, what is the minimum kinetic energy of the cart in the position shown? [Neglect energy loss due to friction.]

1. 4.91 J 3. 250. J

2. 50.0 J 4. 491 J

4 45. A constant force of 1900 newtons is required to keep an automobile having a mass of 1.0 X 103 kilograms moving at a constant speed of 20. meters per second. The work done in moving the automobile a distance of 2.0 X 103 meters is

1. 2.0 X 104 J 3. 2.0 X 106 J

2. 3.8 X 104 J 4. 3.8 X 106 J



1 46. In the diagram shown, 400. joules of work is done raising a 72-newton weight a vertical distance of 5.0 meters. How much work is done to overcome friction as the weight is raised?

1. 40. J 3. 400. J

2. 360 J 4. 760 J



4 47. What is the maximum height to which a 1200-watt motor could lift an object weighing 200. newtons in 4.0 seconds?

1. 0.67 m 3. 6.0 m

2. 1.5 m 4. 24 m

4 48. A spring of negligible mass has a spring constant of 50. newtons per meter. If the spring is stretched 0.40 meter from its equilibrium position, how much potential energy is stored in the spring?

1. 20. J 3. 8.0 J



2. 10. J 4. 4.0 J

4 49. Which graph best represents the elastic potential energy stored in a spring (PEs) as a function of its elongation, x?



1 50. Which graph best represents the relationship between the gravitational potential energy of a freely falling object and the object's height above the ground near the surface of Earth?

1 51. A block weighing 15 newtons is pulled to the top of an incline that is 0.20 meter above the ground, as shown. If 4.0 Joules of work are needed to pull the block the full length of the incline, how much work is done against friction?



1. 1.0 J 3. 3.0 J

2. 0.0 J 4. 7.0 J

2 52. Note: This question has only three choices. As a spring is stretched, its elastic potential energy

1. decreases 3. remains the same

2. increases



1 53. A catapult with a spring constant of 1.0 × 104 newtons per meter is required to launch an airplane from the deck of an aircraft carrier. The plane is released when it has been displaced 0.50 meter from its equilibrium position by the catapult. The energy acquired by the airplane from the catapult during takeoff is approximately

1. 1.3 x 103 J 3. 2.5 x 103 J

2. 2.0 x 104 J 4. 1.0 x 104 J

1 54. In raising an object vertically at a constant speed of 2.0 meters per second, 10. watts of power is developed. The weight of the object is

1. 5.0 N 3. 40. N

2. 20. N 4. 50. N



2 55. The accompanying diagram shows a 5.0-kilogram mass sliding 9.0 meters down an incline from a height of 2.0 meters in 3.0 seconds. The object gains 90. joules of kinetic energy while sliding. How much work is done against friction as the mass slides the 9.0 meters?

2 56. A motor having a power rating of 500. watts is used to lift an object weighing 100. newtons. How much time does the motor take to life the object a



vertical distance of 10.0 meters?

1. 0.500 s 3. 5.00 s

2. 2.00 s 4. 50.0 s

4 57. Which graph best represents the kinetic energy KE of an object as a function of its speed v?





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