1.4 Work done and power
9 exam questions worth 19 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
0 / 19
A force of 40 N moves a trolley 6.0 m in the direction of the force. Calculate the work done.
Mark scheme
W = 40 × 6.0 (1); 240 J (1)
Model answer
W = F s = 40 × 6.0 = 240 J.
State what is meant by a power of 1 watt.
Mark scheme
1 joule of energy transferred per second / 1 J/s
Model answer
One joule of energy transferred every second.
A crane does 9000 J of work lifting a load in 15 s. Calculate the power of the crane.
Mark scheme
P = 9000 / 15 (1); 600 W (1)
Model answer
P = W / t = 9000 / 15 = 600 W.
A 1500 W hairdryer is used for 4 minutes. Calculate the energy transferred in joules.
Mark scheme
4 × 60 = 240 s (1); E = 1500 × 240 (1); 360 000 J (1)
Model answer
Time = 4 × 60 = 240 s. E = P t = 1500 × 240 = 360 000 J.
A cyclist brakes and the bike slows down. Explain why the brake pads get warmer.
Mark scheme
work is done against friction (1); energy is transferred to the thermal store of the brakes (1)
Model answer
Work is done against the force of friction, so energy is transferred from the kinetic store of the bike to the thermal store of the brake pads.
Two motors lift identical loads through the same height. Motor A takes 5 s and motor B takes 10 s. Which statement is correct?
Choose one answer.
Correct Not quite: the answer is A has more power than B
Mark scheme
A: A has more power than B
Model answer
Motor A has more power (A), because it does the same work in less time.
A 60 W lamp is left on for 8.0 hours. Calculate the energy transferred, in kilojoules.
Mark scheme
t = 8.0 × 3600 = 28 800 s (1); E = P t = 60 × 28 800 = 1 728 000 J (1); 1730 kJ (1)
Model answer
t = 8.0 × 3600 = 28 800 s. E = P t = 60 × 28 800 = 1 728 000 J, which is about 1730 kJ.
A student of mass 55 kg climbs a flight of stairs 4.0 m high in 8.0 s. Calculate her power output. (g = 9.8 N/kg)
Mark scheme
work done = m g h = 55 × 9.8 × 4.0 = 2156 J (1); P = W ÷ t = 2156 ÷ 8.0 (1); 270 W (1)
Model answer
W = 55 × 9.8 × 4.0 = 2156 J. P = 2156 / 8.0 = 270 W (to 2 significant figures).
A waiter holds a tray of drinks still, in front of him. Explain why he does no work on the tray.
Mark scheme
work done = force × distance moved in the direction of the force (1); the tray does not move, so the distance is zero and no work is done (1)
Model answer
Work done is force multiplied by the distance moved in the direction of the force. The tray does not move, so the distance is zero and the work done is zero.
Found a mistake?