A motorised roller door is tested before and after oil is applied to its moving joints. The total input energy transfer is 5000 J in each test. The useful energy transfer to raise the door is recorded below.
| Test | Useful energy transfer (J) |
|---|---|
| Before oil is applied | 1600 |
| After oil is applied | 2000 |
Calculate the efficiency of the roller door in each test.
Explain why applying oil changes the efficiency of the roller door.
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.