GCSE Questions: Energy Changes

Q4. The photo shows a lift (elevator) inside a building.

(a) The motor in the lift does 120 000 J of work in 8.0 seconds.
Calculate the power output of the motor in the lift.

[3 marks]

(b) The power input to the motor is greater than the power output.

Tick two reasons why.

Reason Tick
Energy is transferred in heating the surroundings.
Friction causes energy to be transferred in non-useful ways.  
The motor is connected to the mains electricity supply.  
The motor is more than 100% efficient.  
There are only four people in the lift.  


[2 marks]

(c) The diagram shows part of the circuit that operates the lift motor.

The lift can be operated using either of the two switches. Explain why.

[2 marks]

(d) The lift goes up 14 m. The total mass of the people in the lift is 280 kg.

(i) Write down the equation that links gravitational field strength, gravitational potential energy, height and mass.

[1 mark]

(ii) Given that gravitational field strength = 9.8 N/kg, calculate the increase in gravitational potential energy of the people in the lift.

Give your answer to 2 significant figures

[3 marks]

[Total 11 marks]