The visualization above gives a very general idea of what Collisions in 2D look like.
Assume that the masses of the balls is in grams and the magnitude of the velocity is in meters per second.

Here are the two basic equations governing collisions :
1. Linear Momentum is converved. (Linear Momentum of Ball 1 + Linear of Momentum of Ball 2 remains the same before and after collision. )
2.  Relative velocity of approach = -e * Velocity of Separation.

Contributor: Mrinal Mohit, IIT Kharagpur