A motorised stage turntable receives 2.40 kJ of electrical energy each time it moves scenery. Before a modification, it transfers 1.56 kJ usefully to the kinetic energy store of the turntable and scenery.
The table shows every unwanted energy transfer during one movement.
| Unwanted energy transfer | Before modification (kJ) | After modification (kJ) |
|---|---|---|
| Heating caused by friction | 0.36 | 0.21 |
| Heating in electrical connections | 0.30 | ? |
| Sound and unwanted vibration | 0.18 | 0.15 |
The modification reduces the energy transferred by heating in the electrical connections by 40%. The turntable still receives 2.40 kJ for each movement.
Calculate the efficiency of the turntable after the modification.
100 exam-style questions on Edexcel GCSE Physics 3.2 Dissipation and efficiency, covering 3.2.1 Dissipation of energy, 3.2.2 Reducing unwanted energy transfers, 3.2.3 Efficiency, and 3.2.4 Increasing efficiency. Each one has a worked solution and a mark scheme showing where the marks go.