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Physics (AS & A Level) · Oct / Nov 2021 · Paper 13 · Question 17

9702Energy conservation

A mechanical device does useful work at rate X and wastes energy at rate Y. Which expression gives the efficiency of this device?

  1. AX/Y
  2. B(X − Y)/Y
  3. CX/(X + Y)
  4. D(X − Y)/(X + Y)

As printed in the paper

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Correct answer: C. X/(X + Y)

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