A machine takes in 500 J and delivers 350 J of useful output. Its efficiency is
- A. 30%
- B. 43%
- C. 70%
- D. 143%
Explanation
Efficiency is useful output divided by total input times 100, which is 350 over 500 times 100, giving 70%. The remaining 150 J is lost, mostly as heat through friction. An efficiency above 100% is impossible, so the last option can be discarded on principle alone.
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