The gears of a machine are lubricated.
Which statement explains why this increases the efficiency of the machine?
Less work is done against friction, so a greater fraction of the input energy is useful
Less work is done against friction, so the total energy of the machine increases
More work is done against friction, so more energy is transferred to useful stores
The input energy increases, so the useful output energy increases by the same amount
50 exam-style questions on OCR GCSE Physics 7.2 Power and efficiency, covering 7.2.1 Dissipation of energy, 7.2.2 Energy transfers in domestic devices, 7.2.3 Power ratings of domestic appliances, 7.2.4 Efficiency of energy transfers, 7.2.5 Ways to increase efficiency, 7.2.6 Reducing unwanted energy transfers, and 7.2.7 Thermal conductivity and the cooling of buildings. Each one has a worked solution and a mark scheme showing where the marks go.