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

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.

• 450 J

• 4500 J

• 0.045 kJ

• 45 J

• 45 000 J

• 45 kJ

• 4.5 kJ

• 0.45 kJ

Answer explanation

All of the pairs of equivalent values have been correctly matched up.

A force of 600 N is used to lift a box above the ground. An identical box is moved three times as high by a force of 200 N. How much work was done lifting the second box compared to the first?

• 9× less

• 3× less

• the same amount

• 3× more

• 9× more

Answer explanation

The force used to move the second box is 3× bigger (so 3× more work is done) but the distance moved is 3× smaller (so 3× less work is done). Overall, the amount of work done is the same for both boxes.

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

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

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

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

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

Aisha does 480 J of work pushing a crate 6 m along the floor. What is the size of the force that she pushed the crate with?

• 480 ÷ 6 = 80 N

• 480 N

• 480 × 6 = 2,880 N

Answer explanation

Work done = force × distance and so 480 J = force × 6 m. The force is found by dividing both sides of the equation by 6 m.