A powered mechanism opens the vents of a greenhouse. The energy transfers during two tests are shown in the table.
| Test | Total input energy transfer (J) | Useful output energy transfer (J) |
|---|---|---|
| Before lubrication | 5000 | 2000 |
| After lubrication | 5000 | 3500 |
Calculate the increase in the efficiency of the mechanism after lubrication.
Explain why lubrication increased the efficiency of the mechanism, and why the mechanism is still not 100% efficient.
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.