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Homework Help: Collision physics help

  1. Dec 8, 2012 #1
    1. The problem statement, all variables and given/known data

    Cart A, with a mass of 0.20 kg, travels on a horizontal air track at 3.0m/s and hits cart B,
    which has a mass of 0.40 kg and is initially traveling away from A at 2.0m/s. After the collision
    the center of mass of the two cart system has a speed of:
    A. zero
    B. 0.33m/s
    C. 2.3m/s
    D. 2.5m/s
    E. 5.0m/s

    2. Relevant equations

    3. The attempt at a solution

    Vcom = [(0.2)(3)+(0.4)(2)]/(0.2+0.4) = 2.3333

    but ans says its 0.33 m/s? why?
  2. jcsd
  3. Dec 8, 2012 #2
    It seems to me that you might be mis-interpreting the question. If your description of the problem is accurate, then it's easy to see that the answer is not 0.33 m/s. If A bumps into B from behind, the speed of both must be faster than the original speed of B. However, if A and B collide head-on, their center of mass will move at 0.33 m/s.

    If it is the case that B is traveling away from A as you say, then the answer should be 2.3 m/s.
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