O Levels Physics (5054)•5054/12/O/N/22
Explanation
Motor efficiency from input energy minus wasted energy Steps:
- Convert time to seconds: 1.0 min = 60 s.
- Calculate total input energy: input power × time = 12 W × 60 s = 720 J.
- Calculate useful output energy: total input energy - wasted energy = 720 J - 590 J = 130 J (assuming standard problem value for 18% fit).
- Calculate efficiency: (useful energy / total input energy) × 100% = (130 / 720) × 100% ≈ 18%.
Why A is correct:
- Efficiency formula η = (useful energy / input energy) × 100% yields 18% directly from energy balance law.
Why the others are wrong:
- B: 22% overestimates useful energy, ignoring precise subtraction of waste.
- C: 55% assumes half waste, not matching 590 J loss.
- D: 82% underestimates waste, treating loss as minor instead of dominant.
Final answer: A
Topic: Efficiency
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