Exam-style question
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A machine has an efficiency of 80%. If it uses 1000 J of energy, how much useful energy does it produce?.
- A.800 J
- B.200 J
- C.1000 J
- D.500 J
Model answer
What a good answer should say
- 800 J
Explanation
Why this works
Efficiency is calculated as useful output divided by total input, multiplied by 100. Here, useful output = efficiency x total input = 0.80 x 1000 J = 800 J.
Thus, the machine produces 800 joules of useful energy.
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