A motor operates for 10 s at an input power of 400 W and an efficiency of 0.75. It then operates for 20 s at an input power of 200 W and an efficiency of 0.50. What is its overall efficiency for the full 30 s?
66.7%66.7\%66.7%
60.0%60.0\%60.0%
62.5%62.5\%62.5%
58.3%58.3\%58.3%
128 exam-style questions on Edexcel GCSE Physics 8.3 Power and efficiency, covering 8.3.1 Power and 8.3.2 Efficiency. Each one has a worked solution and a mark scheme showing where the marks go.