Impulse-momentum theorem

Steps:

• Mass m = 0.2 kg (converted from 200 g, typical for such problems).
• Change in velocity Δv = 20 m/s (initial) + 10 m/s (rebound) = 30 m/s.
• Change in momentum Δp = m × Δv = 0.2 × 30 = 6 kg·m/s.
• Average force F = |Δp| / Δt = 6 / 0.1 = 60 N.

Why B is correct:

• By the impulse-momentum theorem, average force equals change in momentum divided by contact time, yielding 60 N.

Why the others are wrong:

• A: Assumes Δv = 10 m/s, ignoring rebound direction reversal.
• C: Results from using m = 20 kg, an incorrect unit conversion.
• D: Results from using Δt = 0.01 s and m = 20 kg, double error in units and time.

Final answer: B