Two point particles (m1 and m2) will elastically collide at the origin. Mass m1
will initially move with a positive vx, whereas m2 will do so over the y-axis in the positive y-direction.
This does not reduce the generality of what we will observe, as we can always find a coordinate system with the
y-axis corresponding to the motion of m2 prior to the collision.
Change the masses of the particles and their velocity and see what happens.
Model the collision and predict the motion after the collision.