1. The problem statement, all variables and given/known data The problem and solution is here: http://nebula.deanza.edu/~newton/4A/4AE2P3Winter10.jpg . 2. Relevant equations The equations are in that link. 3. The attempt at a solution My question is how do you know that the final velocities of both masses are equal to each other? wouldnt that ONLY be hte case if the collision was perfectly inelastic (which he didnt mention).