Particle 1 of mass m moving with speed v in the +x direction has an elastic
collision with particle 2 of mass 3m which was originally at rest. After the collision,
particle 2 is moving in the +x direction. What is its speed?
deltap = 0
pf1 + pf2 = pi1 + pi2
The Attempt at a Solution
Wouldn't it just be
pf2 = pi1
3mvf2 = mv1
vf2 = v1/3
How come the answer is v1/2 instead? Help please..