1. The problem statement, all variables and given/known data 2. Relevant equations Total initial momentum = total final momentum Momentum = m*v Kinetic energy = 1/2 * m * v2 3. The attempt at a solution What I found so far: m1v1i = (m1+m2)vf Total kinetic energy = 1/2 * (m1 + m2)vf2 - 1/2 * m1 * v1i2 I am confused on how friction comes into play here. I know that friction is a non-conservative force.