Hello, This concerns a collision between two spherical balls of equal mass and radius. The collision is two dimensional and not completely elastic. The secondary ball begins stationary. The primary ball travels along the horizontal axis with a given velocity. After the collision, the speed and components of velocity of both balls are observed. u0 = initial velocity of primary ball v0 = initial velocity of secondary ball = 0 u1x = horizontal component of velocity of primary ball post collision u1y = vertical component of velocity of primary ball post collision |u1| = post collision speed of primary ball v1x = horizontal component of velocity of secondary ball post collision v1y = vertical component of velocity of secondary ball post collision |v1| = post collision speed of secondary ball The question is about the coefficient of restitution. What is, if any, the relationship between all or some of the above variables in terms of the coefficient of restitution? Or how can we determine the coefficient of restitution from the above variables? Thank you!