Work,power, and energy test

Which of the following is the best example of work being done on an object?

• holding a 50 kg barbell

• keeping a board in place

• lifting a bag of groceries

• pushing on a car that will not move

Answer explanation

Work is a change in energy.

Mechanical energy does not include

• kinetic

• potential

• thermal

Energy due to elevation is

• mechanical

• kinetic

• elastic potential

• gravitational potential

• internal

Energy due to motion is

• mechanical

• kinetic

• elastic potential

• gravitational potential

• internal

When mechanical energy increases

• positive work is done

• no work is done

• negative work is done

A pendulum swings back and forth. What happens to most of its gravitational potential energy at the bottom of its swing?

• It is transformed into inertia.

• It is transformed into thermal energy.

• It is transformed into kinetic energy.

• It is transformed into chemical potential energy.

T or F? Carrying your backpack from one desk to another is an example of doing work.

• true

• false

Answer explanation

Your backpack starts and ends at the same height - GPE doesn't change.

There's no indication that your backpack changes speed - KE doesn't change.

Work is

• a type of mechanical energy

• a transfer of mechanical energy

• a type of thermal energy

• a transfer of thermal energy

Heat is

• a type of mechanical energy

• a transfer of mechanical energy

• a type of thermal energy

• a transfer of thermal energy

You hold a 50 N bag of nails. After 2 seconds, how much work have you done?

• 0 J

• 25 J

• 50 J

• 100 J

Answer explanation

Yes, a force is exerted, but there's no distance moved.