Power as work done against gravity divided by time

Steps:

• Total height climbed: 20 steps × 0.25 m/step = 5 m.
• Work done (gain in potential energy): mgh = 50 kg × 9.8 m/s² × 5 m = 2450 J.
• Time taken: 7 s.
• Average power: work/time = 2450 J / 7 s = 350 W.

Why C is correct:

• Matches the formula for useful power, P = (mgh)/t, where work equals gravitational potential energy gained.

Why the others are wrong:

• A: Underestimates by using incorrect height or g=10 without full calculation.
• B: Likely halves the power, perhaps forgetting total height or using wrong units.
• D: Overestimates by treating as kinetic energy or ignoring time division.

Final answer: C