Work done (W = F × s) | Exit Quiz | Oak National Academy

Which of these stores of energy does friction cause energy to transfer into?

• chemical

• gravitational

• thermal

Answer explanation

Friction cause heating and leads to energy being transferred to the thermal store of the surroundings.

Which two statements describe what happens to energy when it dissipates?

• The energy is used up, so there is none left.

• The energy spreads out into the surroundings.

• The energy is transferred into a thermal store.

• The energy is transferred into a chemical store.

Answer explanation

Friction can cause energy to dissipate into the surroundings by heating. The same amount of energy is still there, but it is more spread out.

240 J of energy is transferred from a chemical store to both a gravitational store and a thermal store. If 80 J is transferred to the gravitational store, how much is transferred to the thermal store?

• A maximum amount of 160 J.

• Exactly 160 J.

• A minimum amount of 160 J.

• It is impossible to tell.

Answer explanation

Energy can be transferred but it cannot be created or destroyed. There was 240 J of energy before the transfer, so there has to be 240 J in total after it. Therefore exactly 160 J of energy must have been transferred to the thermal store.

Match the energy values on the left to the equivalent values on the right.

• 45 000 J

• 4500 J

• 450 J

• 45 J

• 4.5 kJ

• 45 kJ

• 0.045 kJ

• 0.45 kJ

Answer explanation

All of the pairs of equivalent values have been correctly matched up. If the unit is getting bigger (i.e. J → kJ), the number needs to get smaller, and if the unit is getting smaller (i.e. kJ → J), the number needs to get bigger.

A force of 600 N is used to lift a box above the ground. An identical box is moved three times as high by the same size force. How much work was done lifting the second box compared to the first?

• 3× less

• the same amount

• 3× more

Answer explanation

The force used to move the second box the same but the distance moved is 3× bigger, so 3× more work is done.

Put the statements in order of increasing work done on identical boxes, starting with the least work done.

• Moving a box 1.5 m with a force of 12 N.

• Moving a box 3 m with a force of 5 N.

• Moving a box 2 m with a force of 8 N.

• Moving a box 1 m with a force of 17 N.

Answer explanation

Work done = force × distance so the correct order is 5 N × 3 m = 15 J, 8 N × 2 m = 16 J, 17 N × 1 m = 17 J and 12 N × 1.5 m = 18 J.