An industrial mixer receives energy from an electrical supply. The table shows the energy transfers during one minute of operation, before and after its moving parts are lubricated.
| Energy transfer | Before lubrication (kJ) | After lubrication (kJ) |
|---|---|---|
| energy supplied | 72 | 72 |
| energy transferred usefully to the kinetic store of the mixer | XXX | YYY |
| energy transferred by heating due to electrical resistance, excluding heating due to friction | 18 | 18 |
| energy transferred by sound | 2 | 2 |
| energy transferred by heating due to friction | 7 | 1 |
Calculate the values of X X\,X and YYY.
Calculate the increase in the efficiency of the mixer after lubrication. Give your answer as a decimal.
A technician says that lubricating the mixer destroys some of the energy that was previously transferred by heating due to friction.
Explain whether the technician is correct. Use information from the table in your answer.
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.