Evaluating estimates using typical masses and formulas

Steps:

• Assume cyclist mass ≈ 80 kg (person + bike); small car mass ≈ 800 kg.
• Cyclist KE = ½ × 80 × 5² = 1000 J ≈ 1 × 10³ J.
• Car KE = ½ × 800 × 12² ≈ 57,600 J ≈ 6 × 10⁴ J.
• Cyclist momentum = 80 × 5 = 400 kg m/s = 4 × 10² kg m/s.
• Car momentum = 800 × 12 = 9,600 kg m/s ≈ 10⁴ kg m/s.

Why D is correct:

• Car momentum ≈ 10⁴ kg m/s, but D states 2 × 10 kg m/s (= 20 kg m/s), violating p = m v with typical car mass > cyclist mass and higher speed.

Why the others are wrong:

• A matches calculated cyclist KE ≈ 10³ J.
• B is a reasonable order-of-magnitude for car KE (actual ≈ 6 × 10⁴ J).
• C matches calculated cyclist momentum ≈ 4 × 10² kg m/s.

Final answer: D