Average power equals change in kinetic energy divided by time

Steps:

• Convert mass to kg: 0.12 g = 0.00012 kg (standard unit for such calculations).
• Calculate kinetic energy gained from rest: ΔKE = (1/2) m v² = (1/2) (0.00012) (3.0)² = 5.4 × 10^{-4} J.
• Divide by time interval: P = ΔKE / t = 5.4 × 10^{-4} / 0.20 = 2.7 × 10^{-3} W.

Why C is correct:

• It applies the definition of average power as work done (here, ΔKE imparted by legs) divided by time.

Why the others are wrong:

• A overestimates by using full m v² / t instead of (1/2) m v² / t.
• B underestimates by using net impulse / t as "power" without velocity factor.
• D ignores scaling and uses large mass without unit conversion, yielding ~2.7 W.

Final answer: C