WORK, ENERGY & POWER

1. If a system is isolated, the total energy of the system

• Increases constantly.

• Is constant.

• Decreases constantly.

• Depends on the work done on the system.

Each of the boxes shown is pulled for 10 m across a level, frictionless floor by the force given. Which box experiences the greatest change in its kinetic energy?

• A

• C

• E

• B

• D

Rank in order, from largest to smallest, the gravitational potential energies of the balls.

• 1 > 2 = 4 > 3

• 3 > 2 = 4 > 1

• 1 > 2 > 3 > 4

• 3 > 2 > 4 > 1

Starting from rest, a marble first rolls down a steeper hill, then down a less steep hill of the same height. Ignoring friction, for which is it going faster at the bottom?

• Faster at the bottom of the steeper hill

• Faster at the bottom of the less steep hill

• Same speed at the bottom of both hills

• Can’t say without knowing the mass of the marble

A small child slides down the four frictionless slides A–D. Rank in order, from largest to smallest, her speeds at the bottom.

• vD > vA > vB > vC

• vC > vA > vB > vD

• vD > vA = vB > vC

• vA = vB = vC = vD

Four students run up the stairs in the time shown. Which student has the largest power output?

• A

• B

• C

• D

Which requires more work – a person walking up stairs or a person running up stairs?

• walking

• they require equal work

• running

• no work is required for either because the movement is vertical

Which requires more power – a person walking up stairs or a person running up stairs?

• walking

• running

• they require equal power output

• no power is required at all

A basketball that is dropped bounces back up to its original height. Pick the correct energy transformation from the point when it was dropped until it returns to the original height.

• KE --> PE --> Elastic

• KE --> PE --> Elastic --> PE --> KE

• PE --> KE --> Elastic --> KE --> PE

• Elastic --> PE --> KE --> Elastic

How does conservation of energy explain why something that is falling should speed up?

• It gains kinetic energy because it gains potential energy.

• It loses kinetic energy because no work was done on it.

• It gains kinetic energy because it loses potential energy.

• It loses kinetic energy because the Earth gains potential energy.