1. The problem statement, all variables and given/known data two particles of masses m1 and m2 move at speeds u1, u2 respectively collide and fuse. If α is the angle between the two directions of motion before the collision, find an expression for the new mass m, in terms of m1 m2 u1 u2 and α 2. Relevant equations Etot2 = p2c2+m2c4 3. The attempt at a solution (m12 u12 c2 + m1 2 c4)1/2 + (m22 u22 c2 + m22 c4)1/2 = mc2 However this does not take into consideration the angle α, so I am unsure as to where this comes in.