Exam-style question
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What is the efficiency of a machine that has a useful output of 200 J and a total input of 400 J?.
- A.50%
- B.75%
- C.100%
- D.25%
Model answer
What a good answer should say
- 50%
Explanation
Why this works
Efficiency is calculated using the formula: efficiency = (useful output / total input) x 100. Substituting the values: efficiency = (200 J / 400 J) x 100 = 50%.
This shows that the machine converts half of the input energy into useful work.
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