Physics Chapter 7 Review

If an input of 100 J in a pulley system increases the potential energy of a load by 60 J, what is the efficiency of the system? a. 60% b. 40% c. 0% d. 100%

a. 60%

An apple hanging from a limb has potential energy because of its height. If it falls, what becomes of this energy just before it hits the ground? When it hits the ground? a. Immediately before hitting the ground the apple's energy is kinetic energy; when it hits the ground, its energy becomes thermal energy. b. Immediately before hitting the ground the apple's energy is thermal energy; when it hits the ground, its energy becomes kinetic energy. c. Immediately before hitting the ground the apple's energy is potential energy; when it hits the ground, its energy becomes thermal energy. d. Immediately before hitting the ground the apple's energy is kinetic energy; when it hits the ground, its energy becomes potential energy.

a. Immediately before hitting the ground the apple's energy is kinetic energy; when it hits the ground, its energy becomes thermal energy.

When one does twice the work in twice the time, the power expended is _______. View Available Hint(s) a. four times as much b .the same. c. three times as much d. twice as much.

b .the same.

Which requires more work: lifting a 50-kg sack a vertical distance of 2 m or lifting a 25-kg sack a vertical distance of 4 m? a. The 50 kg sack requires more work. b. Both take the same 1000 J. c. The 25 kg sack requires more work. d. The sack lifted 4 m requires more work.

b. Both take the same 1000 J.

Compared with a car moving at some original speed, how much work must the brakes of a car supply to stop a car that is moving twice as fast? How will the stopping distances compare? a. It takes twice the work and twice the stopping distance. b. It takes four times the work and four times the stopping distance. c. It takes half the work and half the stopping distance. d. There is no change in the work and stopping distance.

b. It takes four times the work and four times the stopping distance.

If both sacks in the preceding question are lifted their respective distances in the same time, how does the power required for each compare? How about for the case in which the lighter sack is moved the same distance in half the time? a. Lifted in the same time, the power is the same. The light sack moving in half the time requires half the power. b. Lifted in the same time, the power is the same. The light sack moving in half the time requires double the power. c. Lifted in the same time, the light sack requires twice the power. The light sack moving in half the time requires four times the power as the heavy sack. d. Lifted in the same time, the heavier sack requires twice the power. The light sack moving in half the time requires the same power as the heavy sack.

b. Lifted in the same time, the power is the same. The light sack moving in half the time requires double the power.

When traveling twice as fast your kinetic energy is increased _______. View Available Hint(s) a. by a factor of two. b. by a factor of four. c. by a factor of three. d. not at all.

b. by a factor of four.

When you lift twice the load twice as high, in half the time, the increase in potential energy is _______. View Available Hint(s) a. three times. b. twice as much. c. four times. d. the same.

c. four times.

A car is raised a certain distance in a service-station lift, thus giving it potential energy relative to the floor. If it were raised twice as high, how much more potential energy would it have? a. It would have the exact same potential energy. b. It would have half as much potential energy. c. It would have equal and opposite potential energy. d. It would have twice as much potential energy.

d. It would have twice as much potential energy.

Two cars are raised to the same elevation on service-station lifts. If one car is twice as massive as the other, compare their gains of potential energy. a. Both cars have the same gains of potential energy. b. The car with twice the mass has half the gain of potential energy. c. The less massive car has equal and opposite change of potential energy compared to the more massive car. d. The car with twice the mass has twice the gain of potential energy.

d. The car with twice the mass has twice the gain of potential energy.

The work that is done when twice the load is lifted twice the distance is _______. View Available Hint(s) a. three times as much b. twice as much. c. the same. d. four times as much.

d. four times as much.