A motor drives a fan. A technician measures the total energy input to the motor and the useful energy transferred to the kinetic store of the fan, first with an unlubricated bearing and then after applying oil to the bearing.
| Bearing | Total energy input | Useful energy output |
|---|---|---|
| Unlubricated | 300 J | 90 J |
| Lubricated | 300 J | 120 J |
Calculate the efficiency of the motor and fan when the bearing is lubricated. Give your answer as a percentage.
Explain how the change in efficiency shown in the table is caused by lubricating the bearing.
104 exam-style questions on AQA GCSE Physics 1.2 Conservation and dissipation of energy, covering 1.2.1 Energy transfers in a system and 1.2.2 Efficiency. Each one has a worked solution and a mark scheme showing where the marks go.