1. The problem statement, all variables and given/known data Two particles of masses m and 3m are connected by a light rigid rod. The system rests on a smooth horizontal table, the heavier mass due east of the lighter mass. The heavier mass is projected with initial velocity uj. Find the velocities of the particles when the rod runs north-south. 2. Relevant equations Conservation of momentum, conservation of energy. 3. The attempt at a solution Applying conservation of momentum in the j direction, 3m(u) + m(0) = 3mv + mw. 3u = 3v + w. Conservation of energy, 1/2(3m)u2 = 3mgh +1/2(3m)v2 u2 = 2gh + v2 I've no idea where to go from here. This isn't homework, just a question I came across while revising for exams.