Serway & Jewett — Linear Momentum and Collisions: Problem 53

Two particles with masses \(m\) and \(3m\) are moving toward each other along the x axis with the same initial speeds \(v_i\). Particle \(m\) is traveling to the left, and particle \(3m\) is traveling to the right. They undergo an elastic glancing collision such that particle \(m\) is moving in the negative y direction after the collision at a right angle from its initial direction. (a) Find the final speeds of the two particles in terms of \(v_i\). (b) What is the angle \(\theta\) at which the particle \(3m\) is scattered?