1. The problem statement, all variables and given/known data Two billiard balls, one heading north at 15.0 m/s and a second heading south at 10.0 m/s, collide head-on. Take the collision to be perfectly elastic and choose the positive direction north. What is the post-impact speed of the first ball Answer: m/s What is the post-impact speed of the second ball? Answer: m/s 2. Relevant equations 3. The attempt at a solution Don't even know where to start.