An automatic sliding door takes 8.0 s to open. Its mean useful power output is 250 W and 400 J of energy is dissipated while it opens. What is the mean input power of the door?
250 W250\ \mathrm{W}250 W
650 W650\ \mathrm{W}650 W
200 W200\ \mathrm{W}200 W
300 W300\ \mathrm{W}300 W
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.