7.1

7.2

7.3

7.4

W = F x d

W = F x 0 = 0

7.5

Power = work / time

PE KE PE = mghKE = ½ mv2

7.6

PE KE

PE = mghKE = ½ mv2

7.7

PE KE

PE = mghKE = ½ mv2

7.8

7.9

7.10

-- Questions --

MULTIPLE CHOICE.

Choose the one alternative that best completes the statement or

answers the question.

7.11

1) If the speed of a moving object doubles, then what else doubles? A) acceleration B) kinetic energy C) momentum D) all of these E) none of these

A small ball tied to a string swings without air resistance, beginning from rest at point A. The string snags on a nail at point P, causing the ball to move in a small circle.

2) The ball has maximum speed at point A) A. B) B. C) C. D) D. E) E.

7.12

3) Two pool balls, each moving at 2 m/s, roll toward each other and collide. Suppose after bouncing apart, each moves at 4 m/s. This collision violates conservation of A) momentum. B) kinetic energy. C) both of these. D) none of these.

4) A woman lifts a box from the floor. She then moves with constant speed to the other side of the room, where she puts the box down. How much work does she do on the box while walking across the floor at constant speed? A) zero J B) more than zero J C) more information needed to determine

7.13

5) If an object has kinetic energy, then it also must have A) momentum. B) acceleration. C) force. D) impulse. E) none of these.

6) A 2-kg mass is held 4 m above the ground. What is the approximate potential energy of the mass with respect to the ground? A) 20 J B) 40 J C) 60 J D) 80 J E) none of these.

7.14

7) A jack system will increase the potential energy of a heavy load by no more than 1000 J with a work input of 2000 J. The efficiency of the jack system is no more than A) 10%. B) 20%. C) 50%. D) 80%. E) not enough information given.

8) A TV set is pushed a distance of 2 m with a force of 20 N that is in the same direction as the set moves. How much work is done on the set? A) 2 J B) 10 J C) 20 J D) 40 J E) 80 J

7.15

9) An object at rest may have A) speed. B) energy. C) momentum. D) velocity. E) none of these.

10) If you push an object twice as far while applying the same force you do

A) the same amount of work. B) four times as much work. C) twice as much work.

7.16

11) A sandbag in outer space moves at 3 m/s and collides and sticks to a half-as-massive sandbag initially at rest. Compared to the kinetic energy of the moving bag before collision, the kinetic energy of the coupled bags after collision is A) three quarters. B) two thirds. C) one third. D) not enough information to say.

12) A car that travels twice as fast as another when braking to a stop will skid A) twice as far. B) four times as far. C) depends on the mass of the cars.

7.17

13) Two 5000-kg freight cars roll without friction (one at 1 m/s, the other at 2 m/s) toward one another on a level track. They collide, couple, and roll away together with a combined momentum of A) zero. B) 15,000 kg m/s. C) 10,000 kg m/s. D) 5000 kg m/s.

14) An open freight car rolls friction free along a horizontal track in a pouring rain that falls vertically. As water accumulates in the car, the car's speed A) doesn't change. B) increases. C) decreases.

7.18

A small bead slides without friction along the wire shown here, beginning at point A. The wire does not touch itself at point C, so the bead has room to slide past that point.

15) The bead has maximum potential energy at point A) A. B) B. C) C. D) D. E) F.

7.19

-- Answers --

MULTIPLE CHOICE.

The one alternative that best completes the statement or

answers the question.

7.20

Chapter 7

1) Answer: C 2) Answer: B 3) Answer: B 4) Answer: A 5) Answer: A 6) Answer: D 7) Answer: C 8) Answer: D 9) Answer: B 10) Answer: C 11) Answer: B 12) Answer: B 13) Answer: D 14) Answer: C 15) Answer: A