Two particles with masses 2m and 6m are moving toward each
other along the x axis with the same initial speeds vi.
Particle 2m is traveling to the left, while particle 6m
is traveling to the right. They undergo an
elastic, glancing collision such that particle 2m is moving
downward after the collision at a right angle from its initial
direction. What is the angle θ at which the particle
6m is scattered from its original path?