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GCSE Questions: Energy Changes

Q10. The diagram shows Trudi doing an experiment to determine her power output by running to the top of some stairs.

(a) Trudi's mass was 60.0 kg.

The height of the stairs was 175 cm.

She ran to the top of the stairs in 1.40 s.

Given that the gravitational field strength = 9.8 N/kg, calculate Trudi's power output.

Change in Gravitational Potential Energy = Mass x Gravitational Field Strength x change in vertical height

Δ EG = mgΔh

Δh = 175 cm = 1.75 m

Δ EG = 60.0 x 9.8 x 1.75= 1029 J

Power = Energy/time

Power = 1029/1.4 = 735 W

[5 marks]

(b) Trudi's total power output was greater than the answer to part (a).

Suggest two reasons why.

Trudi increases her kinetic energy (as well as increasing her gravitational potential energy) when she runs up the stairs. Some energy is also transferred as thermal energy to the surroundings.

[2 marks]

(c) Tony took more than 1.40 s to run up the same stairs but his power output was the same as Trudi's. What conclusion can be made about Tony's mass?

His mass must be greater than Trudi's.

[1 mark]

[Total 8 marks]