Estimating kinetic energy with KE = ½mv²

Steps:

• Assume athlete mass m ≈ 75 kg (typical for sprinter).
• Estimate top speed v ≈ 12 m/s (elite 100m pace).
• Compute v² = 144 m²/s².
• Calculate KE = ½ × 75 × 144 = 5400 J, closest to 4000 J.

Why C is correct:

• 4000 J aligns with KE formula using realistic mass (70–80 kg) and sprint speed (11–13 m/s), yielding 4000–6000 J.

Why the others are wrong:

• A: 40 J is kinetic energy of a small thrown object, not a 75 kg human.
• B: 400 J suits a slow-moving child (v ≈ 3 m/s), far below sprint speeds.
• D: 40000 J implies unrealistically high speed (v ≈ 36 m/s) or mass (500 kg).

Final answer: C