Kinetic Energy from Mass and Speed

Steps:

• Estimate athlete's mass at 75 kg, typical for sprinters.
• Use maximum speed of about 12 m/s from elite 100m races.
• Apply formula KE = ½ mv²: ½ × 75 × 12² = ½ × 75 × 144 = 5400 J.
• Round to nearest order of magnitude: approximately 4000 J.

Why B is correct:

• 4000 J aligns with KE = ½ mv² using realistic mass (75 kg) and speed (12 m/s) for Olympic runners.

Why the others are wrong:

• A: 400 J is too low, like energy of a thrown baseball, not a running human.
• C: 40000 J is too high, akin to a small car's impact energy.
• D: 400000 J vastly overestimates, comparable to a motorcycle's kinetic energy.

Final answer: B