Question 7
Newton's Laws and MomentumA body of mass 12 kg travelling at 4.2 ms−1 collides with a second body of mass 18 kg at rest. Calculate their common velocity if the two bodies coalesce after collision.
- A.1.5 ms−1.
- B.1.4 ms−1.
- C.2.1 ms−1.
- D.1.7 ms−1.
Show the answer and explanation
Answer: D (1.7 ms−1.)
Explanation
Momentum is conserved: 12 × 4.2 = (12 + 18)v, so v = 50.4 ÷ 30 = 1.68 ≈ 1.7 m s−1.