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Chapter 6 (Energy)
1. 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
2. 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 d. 2000 J
3. A 7 kg bowling ball falls from a 2.0 m shelf. Just before hitting the floor, what will be its kinetic energy? (g = 9.8 m/s2 and assume air resistance is negligible.)
a. 14 J b. 19.6 J c. 29.4 J d. 137 J
4. An rock is thrown straight up with an initial velocity of 15 m/s. Ignore energy lost to air friction. How high will the rock rise?
a. 1.4 m b. 2.4 m c. 6.5 m d. 11.5 m
5. What is the minimum amount of energy required for an 80‑kg climber carrying a 20‑kg pack to climb Mt. Everest, 8850 m high?
a. 8.67 MJ b. 4.16 MJ c. 2.47 MJ d. 1.00 MJ
6. A professional skier reaches a speed of 56 m/s on a 30˚ ski slope. Ignoring friction, what is the minimum distance along the slope the skier would have to travel, starting from rest?
a. 110 m b. 160 m c. 320 m d. 640 m
7. 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 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 8. Adisa pulls a 40 N crate up a 5 m 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 gain in potential energy by the crate in the process?
a. 120 J b. ‑120 J c. 200 J d. ‑200 J
9. 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 velocity 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. 4.6 m/s
10. 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.
11. Which of the following is that form of energy associated with an object’s motion?
a. potential b. thermal c. big‑chemical d. kinetic
12. Which of the following is that form of energy associated with an object’s location in a conservative force field?
a. potential b. thermal c. bio‑chemical d. kinetic
13. 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
14. 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 object’s kinetic energy?
a. decreases b. increases c. remains constant d. cannot tell form the information given
15. 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
16. 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 object’s kinetic energy c. increases the object’s potential energy d. None of the above choices are valid.
17. The unit of work, Joule, is dimensionally the same as:
a. Newton/second b. Newton/kilogram c. Newton‑second d. Newton‑meter
18. The unit of power, Watt, is dimensionally the same as:
a. Joule‑second b. Joule/second c. Joule‑meter d. Joule/meter
19. Rupel pushes a box 5 m by applying a 25 N horizontal force. What work does she do?
a. 10 J b. 25 J c. 125 J d. 550 J
20. A worker pushes a sled with a force of 40 N over a level distance of 6 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
21. Samanthat 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 22. Preston pushes a 500 N weight wheelbarrow to the top of a 50.0 m ramp, inclined at 20˚ with the horizontal, and leaves it. Tamara accidentally bumps the wheelbarrow. It slides back down the ramp, during which a 80 N frictional force acts on it over the 50.0 m. What is the wheelbarrow’s kinetic energy at the bottom at of the ramp? (g = 9.8 m/s2)
a. 4550 J b. 6550 J c. 8150 J d. 13100 J
23. What is the kinetic energy of a 0.135 kg baseball thrown at 40 m/s (90 mph)?
a. 54 J b. 87 J c. 108 J d. 216 J
24. 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/s2)
a. 221 J b. 688 J c. 10.2 J d. 100 J
25. 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 at the bottom of the ramp? (g = 9.8 m/s2)
a. 6.1 m/s b. 3.5 m/s c. 10.7 m/s d. 8.3 m/s
26. A pile driver drives a post into the ground. The mass of the pile driver is 2500 kg and it is dropped through a height of 8 m on each stroke. If the resisting force of the ground is 4 ´ 106 N, how far is the post driven in on each stroke?
a. 4.9 cm b. 9.8 cm c. 16.0 cm d. 49.0 cm
27. A 2000‑kg ore car rolls 50 meters down a frictionless 10˚ 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 meter?
a. 340.3 kN/m b. 680.7 kN/m c. 980.0 kN/m d. 1960.0 kN/m
28. 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‑gram marble?
a. 14 m/s b. 15.2 m/s c. 18.3 m/s d. 21.3 m/s
29. A 60‑kg woman runs up a flight of stairs having a rise of 4 meters in a time of 4.2 seconds. What average power did she supply?
a. 380 W b. 560 W c. 616 W d. 672 W
30. 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. 4500 J
31. 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 force of friction acts to retard the motion of the cart?
a. 110 N b. 90 N c. 80 N d. 70 N
32. 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 catcher’s glove 1.0 m above the ground? (g = 9.8 m/s2 and ignore air resistance.)
a. 44.3 m/s b. 38.0 m/s c. 31.3 m/s d. 22.2 m/s
33. A baseball catcher puts on an exhibition by catching a 0.15 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 0.75 m while catching it, what average force is exerted on the mitt by the ball? (g = 9.8 m/s2)
a. 78 N b. 119 N c. 196 N d. 392 N
34. A simple pendulum, 1.0 m in length, is released from rest when the support string is at an angle of 35˚ from the vertical. What is the speed of the suspended mass at the bottom of the swing? (Ignore air resistance, g = 9.8 m/s2)
a. 0.67 m/s b. 0.94 m/s c. 1.33 m/s d. 1.88 m/s
35. 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/s2)
a. 2.3 m/s b. 2.6 m/s c. 2.0 m/s d. 0.5 m/s
36. 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˚
37. An automobile delivers 30 hp to its wheels when moving at a constant speed of 22 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
38. I use a rope 2 m long to swing a 10 kg weight around my head. The tension in the rope is 20 N. In half a revolution how much work is done by the rope on the weight?
a. 40 J b. 126 J c. 251 J d. 0
39. The work done by static friction is always:
a. positive b. negative c. along the surface d. zero
40. 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
41. 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. It did not lose kinetic energy.
42. 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
43. A 2 kg ball has zero kinetic and potential energy. Ernie drops the ball into a 10 m deep well. Just before the ball hits the bottom, the sum of its kinetic and potential energy is:
a. 0 b. 196 J c. ‑196 J d. 392 J
44. A 2 kg ball has zero potential and kinetic energy. Maria drops the ball into a 10 m deep well. After the ball comes to a stop in the mud, the sum of its potential and kinetic energy is:
a. 0 b. 196 J c. ‑196 J d. 392 J
45. 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.
46. A girl and her bicycle have a total mass of 40 kg. At the top of the hill her speed is 5 m/s and her speed doubles as she rides down the hill. The hill is 10 m high and 100 m long. How much kinetic energy and potential energy is lost to friction?
a. 2420 J b. 1500 J c. 2000 J d. 3920 J 47. A girl and her bicycle have a total mass of 40 kg. At the top of the hill her speed is 5 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 m/s b. 10 m/s c. 11 m/s d. She stops before she reaches the bottom.
48. Old Faithful geyser in Yellowstone Park shoots water hourly to a height of 40 meters. With what velocity does the water leave the ground?
a. 7.0 m/s b. 14.0 m/s c. 19.8 m/s d. 28.0 m/s
49. An 80,000 kg airliner is flying at 900 kilometers/hour at a height of 10 kilometers. What is its total energy (kinetic + potential)?
a. 250 MJ b. 478 MJ c. 773 MJ d. 10,340 MJ
50. A 1200 kg automobile moving at 25 m/s has the brakes applied with a deceleration of 8 m/s2. How far does the car travel before it stops?
a. 39 m b. 47 m c. 55 m d. 63 m
51. I drop a 60 g golfball from 2 m high. It rebounds to 1.5 m. How much energy is lost?
a. 0.29 J b. 0.5 J c. 0.88 J d. 1 J
52. Yuriy, a Russian weightlifter, is able to lift 250 kg 2 m in 2 s. What is his power output?
a. 500 W b. 2.45 kW c. 4.9 kW d. 9.8 kW
53. A jet engine develops 105 N of thrust in moving an airplane forward at a speed of 900 km/hr. What is the power developed by the engine?
a. 500 kW b. 1 MW c. 2.5 MW d. 5 MW 54. 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. 2667 N b. 5333 N c. 6500 N d. 7711 N
55. A pole vaulter clears 6 m. With what velocity does he strike the mat in the landing area?
a. 2.7 m/s b. 5.4 m/s c. 10.8 m/s d. 21.6 m/s
56. A parachutist of mass 50 kg jumps out of an airplane at a height of 1000 m. The parachute deploys, and she lands on the ground with a velocity of 5 m/s. How much energy was lost to air friction during this jump?
a. 49,375 J b. 98,750 J c. 197,500 J d. 489,375 J
57. Water flows over a section of Niagara Falls at a rate of 1.2 ´ 106 kg/s and falls 50 m. What is the power wasted by the waterfall?
a. 588 MW b. 294 MW c. 147 MW d. 60 MW
58. 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
59. 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
60. A 1000 kg sportscar 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
Chapter 6 ‑ Answers
# Ans Difficulty # Ans Difficulty
1. C 1 31. B 2 2. A 1 32. A 2 3. D 1 33. C 2 4. D 2 34. D 2 5. A 2 35. A 2 6. C 2 36. B 2 7. D 2 37. C 2 8. A 2 38. D 2 9. D 2 39. D 1 10. C 1 40. C 1 11. D 1 41. C 1 12. A 1 42. D 1 13. D 1 43. A 1 14. A 1 44. C 2 15. B 1 45. C 1 16. D 1 46. A 2 17. D 1 47. C 2 18. B 1 48. D 3 19. C 1 49. D 2 20. D 1 50. A 2 21. D 1 51. A 2 22. A 2 52. B 2 23. C 1 53. C 2 24. D 1 54. B 2 25. B 2 55. C 2 26. A 2 56. D 2 27. A 1 57. A 3 28. A 2 58. C 3 29. B 2 59. D 2 30. C 1 60. C 2
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