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Physics (AS & A Level) · Oct / Nov 2019 · Paper 11 · Question 15

9702Energy conservation

An electric motor produces 120 W of useful mechanical output power. The efficiency of the motor is 60%. Which row is correct?

  1. Aelectrical power input 72 W, waste heat power output 48 W
  2. Belectrical power input 192 W, waste heat power output 72 W
  3. Celectrical power input 200 W, waste heat power output 72 W
  4. Delectrical power input 200 W, waste heat power output 80 W

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Correct answer: D. electrical power input 200 W, waste heat power output 80 W

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