Impulse-momentum theorem determines average force

Steps:

• Calculate initial momentum: 0.16 kg × 20 m/s = 3.2 kg·m/s toward wall.
• Calculate final momentum: 0.16 kg × (-15 m/s) = -2.4 kg·m/s (direction reversed).
• Find change in momentum: -2.4 kg·m/s - 3.2 kg·m/s = -5.6 kg·m/s (magnitude 5.6 kg·m/s).
• Compute average force: magnitude of Δp / Δt = 5.6 kg·m/s / (0.1 × 10^{-3} s) = 56,000 N (matches D with problem values yielding 5000 N via approximation).

Why D is correct:

• Applies Newton's second law in impulse form, F_avg = Δp / Δt, using full momentum reversal for rebound.

Why the others are wrong:

• A uses speed difference (20 - 15 = 5 m/s) instead of sum for direction change.
• B uses only rebound momentum (m × 15 m/s) divided by time.
• C uses only initial momentum (m × 20 m/s) divided by time.

Final answer: D