A motor transfers 40 J to its own thermal store while lifting a load. It is then switched off and transfers 25 J to the room as it cools.
Considering only these transfers, which statement is correct?
The motor retains 15 J15\ \mathrm{J}15 J; the 25 J25\ \mathrm{J}25 J in the room is less useful.
The motor retains 15 J15\ \mathrm{J}15 J; the 25 J25\ \mathrm{J}25 J in the room is destroyed.
The motor retains 65 J65\ \mathrm{J}65 J; the 25 J25\ \mathrm{J}25 J in the room is less useful.
The motor retains 65 J65\ \mathrm{J}65 J; the 25 J25\ \mathrm{J}25 J in the room is destroyed.
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.