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GRE Momentum question debate

  1. Sep 28, 2013 #1
    1. The problem statement, all variables and given/known data


    The question hasn't been typed up yet but it's pretty basic. A particle of mass m runs into a particle of mass 2m. After the collision, the particle with m is at rest and the particle of mass 2m has split into two particles each with mass that have both y and x components to their velocity, separated by θ.

    If you look at the people that commented on this question there seems to be a bit of debate. One quite intelligent and confident poster wrote that the velocity in the x direction for each particle is equal to v/2, since the initial velocity was v and horizontal momentum must be conserved. Another poster wrote that the x component of velocity for each particle does NOT equal v/2 because they aren't moving along the x-axis.

    Who is correct and why?

    Thanks Physics Forums!
  2. jcsd
  3. Sep 28, 2013 #2

    Doc Al

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    Staff: Mentor

    A full statement of the problem would help. The angle θ is the angle between the two split particles or is the angle they both make with the original direction of the first particle (as one comment assumed)?

    Why couldn't the x-components be v/3 and 2v/3? Unless the split is symmetric.

    I don't know what that is supposed to mean. I assume that the x-axis is the direction of motion of the first particle.
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