Chapter 07

# Chapter 07 - Chapter 7: KINETIC ENERGY AND WORK 1. Which of...

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Chapter 7: KINETIC ENERGY AND WORK 1. Which of the following is NOT a correct unit for work? A. erg B. ft · lb C. watt D. newton · meter E. joule ans: C 2. Which of the following groups does NOT contain a scalar quantity? A. velocity, force, power B. displacement, acceleration, force C. acceleration, speed, work D. energy, work, distance E. pressure, weight, time ans: B 3. A boy holds a 40-N weight at arm’s length for 10 s. His arm is 1 . 5 m above the ground. The work done by the force of the boy on the weight while he is holding it is: A. 0 B. 6 . 1J C. 40 J D. 60 J E. 90 J ans: A 4. A crate moves 10 m to the right on a horizontal surface as a woman pulls on it with a 10-N force. Rank the situations shown below according to the work done by her force, least to greatest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................... . . . . . . . . . . . . 10 N 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 N 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 N 3 A. 1, 2, 3 B. 2, 1, 3 C. 2, 3, 1 D. 1, 3, 2 E. 3, 2, 1 ans: E 86 Chapter 7: KINETIC ENERGY AND WORK

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5. An object moves in a circle at constant speed. The work done by the centripetal force is zero because: A. the displacement for each revolution is zero B. the average force for each revolution is zero C. there is no friction D. the magnitude of the acceleration is zero E. the centripetal force is perpendicular to the velocity ans: E 6. An object of mass 1 g is whirled in a horizontal circle of radius 0 . 5 m at a constant speed of 2m / s. The work done on the object during one revolution is: A. 0 B. 1 J C. 2 J D. 4 J E. 16 J ans: A 7. The work done by gravity during the descent of a projectile: A. is positive B. is negative C. is zero D. depends for its sign on the direction of the y axis E. depends for its sign on the direction of both the x and y axes ans: A 8. A baseball is hit high into the upper bleachers of left f eld. Over its entire F ight the work done by gravity and the work done by air resistance, respectively, are: A. positive; positive B. positive; negative C. negative; positive D. negative; negative E. unknown since vital information is lacking ans: D 9. A line drive to the shortstop is caught at the same height as it was originally hit. Over its entire F ight the work done by gravity and the work done by air resistance, respectively, are: A. zero; positive B. zero; negative C. positive; negative D. negative; positive E. negative; negative ans: B Chapter 7: KINETIC ENERGY AND WORK 87
10. A 2-kg object is moving at 3 m / s. A 4-N force is applied in the direction of motion and then removed after the object has traveled an additional 5 m. The work done by this force is: A. 12 J B. 15 J C. 18 J D. 20 J E. 38 J ans: D 11. A sledge (including load) weighs 5000 N. It is pulled on level snow by a dog team exerting a horizontal force on it. The coe cient of kinetic friction between sledge and snow is 0 . 05. How much work is done by the dog team pulling the sledge 1000 m at constant speed? A. 2 . 5 × 10 4 J B. 2 . 5 × 10 5 J C. 5 . 0 × 10 5 J D. 2 . 5 × 10 6 J E. 5 . 0 × 10 6 J ans: B 12. Camping equipment weighing 6000 N is pulled across a frozen lake by means of a horizontal rope. The coe cient of kinetic friction is 0 . 05. The work done by the campers in pulling the equipment 1000 m at constant velocity is: A. 3 . 1 × 10 4 J B. 1 . 5 × 10 5 J C. 3

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## Chapter 07 - Chapter 7: KINETIC ENERGY AND WORK 1. Which of...

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