Energy transfer

Energy can be created but not stored.

• True

• False

An object that is hotter than its surroundings will...

• emit more radiation than it absorbs

• absorbs more radiation than it emits

• will not absorb radiation

Hot air rises above cold air in a room. This is because the density of the hot air is

• higher than the density of the cold air

• equal to the density of the cold air

• lower than the density of the cold air

What happens to the kinetic energy store of a car when it slows down?

• Remains constant.

• It decreases as some energy is transferred away to different energy stores.

• It decreases as some energy is destroyed

• It increases because the velocity has decreased.

800J of energy is supplied to a toaster through an electrical pathway. The efficiency of the toaster is 25%. How much energy is transferred usefully by the toaster?

• 200

• 600J

• 1000J

• 200J

Energy can be transferred by convection in

• solids

• liquids

• fluids (both liquids and gases)

250J of energy is supplied to a fan. The fan transfers 100J of this energy to useful energy stores. What is the efficiency of the fan?

• 10%

• 40%

• 60%

A convection current in a liquid is caused by density changes in the liquid as its temperature changes.

• True

• False

When an object drops, the energy transfers are...

• kinetic and gravitational stores are filled

• kinetic store depletes, gravitational store fills.

• kinetic and gravitational stores are depleted.

• kinetic store fills, gravitational store depletes.

When a racket hits a ball, energy is transferred from the racket's kinetic store to the ball's kinetic store. This is transferred...

• by a heating pathway

• by a mechanical pathway

• by an electrical pathway

• by a radiation pathway