Work, GPE, KE and power – IGCSE Physics exam questions with mark scheme

1Grade 4–55 marks

A crane lifts a load of weight 800 N through a vertical height of 12 m in 16 s.

(a) Calculate the work done by the crane on the load. [3]

(b) Calculate the useful power output of the crane. [2]

(a) work done = force × distance moved (in direction of force) or $W = Fd$(1)
(a) $W = 800 \times 12$(1)
(a) 9600 J(1)
(b) power = work done ÷ time or $P = \dfrac{9600}{16}$ allow ecf from (a)(1)
(b) 600 W(1)
Answer: (a) 9600 J (b) 600 W
Examiner tip: The weight (800 N) is already a force — do not multiply by g again.

2Grade 6–75 marks

A ball of mass 0.25 kg is dropped from a height of 5.0 m. Air resistance can be ignored.

gravitational field strength $g$ = 10 N/kg

(a) Calculate the gravitational potential energy lost by the ball as it falls 5.0 m. [2]

(b) Calculate the speed of the ball just before it hits the ground. [3]

(a) GPE = $mgh$ or $0.25 \times 10 \times 5.0$(1)
(a) 12.5 J allow 13 J(1)
(b) KE gained = GPE lost or $\tfrac{1}{2}mv^2 = 12.5$ allow ecf from (a)(1)
(b) $v^2 = \dfrac{2 \times 12.5}{0.25} = 100$(1)
(b) 10 m/s(1)
Answer: (a) 12.5 J (b) 10 m/s
Examiner tip: Remember the ½ in KE = ½mv² and take the square root at the end — v² = 100 is not the speed.

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