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A student sets up an experiment to measure the momentum of a system of two air cars, A and B, of equal mass, moving on a linear, frictionless track. Before the collision, car A has a certain speed, and car B is at rest. Which of the following will be true about the total momentum of the two cars?
  1. It will be greater before the collision.
  2. It will be equal before and after the collision.
  3. It will be greater after the collision.
  4. The answer depends on whether the collision is elastic or inelastic.
Question by OpenStax is licensed under CC BY 4.0.
Solution Video

OpenStax College Physics for AP® Courses Solution, Chapter 8, Problem 17 (Test Prep for AP® Courses) (0:29)

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Video Transcript
This is College Physics Answers with Shaun Dychko. The law of the conservation of momentum tells us that the total momentum before collision will be the same as the total momentum after collision, assuming you have a isolated closed system in which no external forces are acting which is true in this case because we have a frictionless track. So momentum should be conserved and that means the total momentum will be equal before and after the collision.