1. The problem statement, all variables and given/known data http://grephysics.net/ans/0177/55 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!