1. The problem statement, all variables and given/known data A 45g marble collides with an identical stationary marble, and continues at 55 degrees to it's original direction. The collision is perfectly elastic. What is the angle between the direction taken by the target ball and the original direction of the incident ball? 2. Relevant equations 3. The attempt at a solution Since elastic collisions in 2 dimensions result in 2 perpendicular velocities after the collision, I'm getting the feeling that the answer is simply 90-55=35 degrees. Is this right?