Power as rate of gravitational potential energy gain

Steps:

• Total height = 30 steps × 0.20 m/step = 6.0 m
• Change in PE = mgh = 75 kg × 9.8 m/s² × 6.0 m = 4410 J
• Time interval = 7.0 s
• Average power = ΔPE / Δt = 4410 J / 7.0 s = 630 W

Why C is correct:

• Power is the rate of work done against gravity, given by ΔPE / time with g = 9.8 m/s².

Why the others are wrong:

• A: Uses g = 10 m/s², yielding ≈642 W.
• B: Likely errors in height (e.g., 15 m) or mass calculation.
• D: ΔPE value (4410 J) without dividing by time.

Final answer: C