The questions are on the work and power test. Take it under real conditions before reading the mark scheme.
Quick answer: Work is the energy transferred when a force moves an object, found from W = F × d and measured in joules. This mark scheme gives the model answers and the marks for the 8 questions of the Physics 9-10 test on work and power, from equations to unit of power, with the equivalent answers to accept.
Model answers and mark schemes follow. Award marks for the equation or method, for correct substitution and for the answer with its unit. Accept equivalent wording and give follow-through marks for consistent errors carried from earlier parts.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS3-1
Question 2 Pushing a mower (3 marks)
- W = F × d = 80 × 25 = 2000 J.
- P = W ÷ t = 2000 ÷ 40 = 50 W.
Marking: (a) 1 mark. (b) 1 mark for substitution, 1 mark for answer with unit.
Question 3 Motorcycle (3 marks)
- KE = ½ × 220 × 15² = ½ × 220 × 225 = 24 750 J.
- Speed doubled, so KE × 4 = 99 000 J.
Marking: (a) 1 mark for substitution, 1 mark for answer. (b) 1 mark.
Question 4 Ball thrown upwards (2 marks)
GPE = m g h = 0.20 × 9.8 × 6.0 = 11.8 J (11.76 J).
Marking: 1 mark for substitution, 1 mark for the answer with unit.
Question 5 Stretching a spring (3 marks)
- The work is the area of the triangle: ½ × 0.50 × 40 = 10 J.
- The work done (energy transferred) in stretching the spring.
Marking: (a) 1 mark for ½ × base × height, 1 mark for answer. (b) 1 mark.
Question 6 Stopping distance (4 marks)
- KE = ½ × 900 × 10² = 45 000 J.
- Work by brakes = KE, so d = 45 000 ÷ 3000 = 15 m.
Marking: (a) 1 mark for substitution, 1 mark for answer. (b) 1 mark for using F × d = KE, 1 mark for answer.
Question 7 Carrying a bag (2 marks)
The upward force acts at right angles to the horizontal movement. Work is only done by the part of a force in the direction of movement, so the distance moved in the direction of the force is zero and the work done by it is zero.
Marking: 1 mark for right angles / no movement along the force, 1 mark for work = force × distance in the direction of the force.
Question 8 Unit of power (1 mark)
The watt: 1 W = 1 J/s.
Marking: 1 mark for joules per second.
