AP Physics 1 Question 230: Answer and Explanation

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Question: 230

11. Object 1 moves with an initial speed of v0 toward Object 2, which has a mass half that of Object 1. If the final speed of both objects after colliding is 0, what must have been the initial speed of Object 2 (assuming no external forces)?

  • A. v0
  • B. 2v0
  • C. v0
  • D. 4v0

Correct Answer: B



Total linear momentum is conserved in the absence of external forces. If the final speed of both objects is 0, that means the total linear momentum after the collision is 0, which then implies that the total linear momentum before the collision is also 0. As Object 2 has half the mass of Object 1, Object 2 must have twice the initial speed of Object 1 (and must be travelling in the opposite direction) in order for the total linear momentum to equal 0.