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