A student investigates how the efficiency of an electric motor depends on the mass of the load it lifts.

The Figure shows the apparatus.

Figure

The motor raises each load through a height of 0.80 m.

The joulemeter measures the total energy supplied to the motor.

The Table shows the results.

Table

Mass of load in $kg\text{kg}$	Total energy supplied to the motor in $J\text{J}$
0.10	8.0
0.20	8.8
0.30	9.6
0.40	10.4
0.50	11.2

Gravitational field strength ( $g$ ) = 10 N/kg

Explain how the efficiency of the motor changes as the mass of the load increases.

You should use calculations based on the data in the Table in your answer.

8 Energy – forces doing work

8 Energy – forces doing work Questions