O-LevelPhysicsEnergy & Work5054/21 · May/June 2025 · Q38 Marks

A battery, a pulley and a motor are used to lift a load as shown in Fig. 3.1. [Figure 3.1]

(a)Describe the transfers between energy stores that occur as the load is lifted.[3]
(b)(i)The efficiency of the motor, pulley and load system is less than 100%. By comparing the input energy and the useful output energy, explain why the efficiency is less than 100%.[1]
(b)(ii)Explain how the principle of conservation of energy applies in lifting the load.[2]
(c)The input power to the motor is 15W. The motor is used for 20s. The efficiency of the motor is 60%. Calculate the energy supplied to the load. energy = .................................................... J[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.

[B3] reduction in chemical energy store in battery
[B3] electrical work done by motor
[B3] mechanical work done on weight
[B3] increase in gravitational energy store of weight
[B3] increase in thermal energy (in motor or air)
[B3] electrical heating (by current)
[B1] useful or output energy < input energy
[B1] total energy is constant
[B1] energy from power supply = energy gained by weight + thermal energy (to air / due to friction)
[C1] (E =) power x time in any form
[A1] 180 J

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