This is a VERY INFORMATIVE video about how mometum works! :DD
With different mass balls, the final speeds of the two balls will also be different. How do you find the speeds of the balls after the collision? One way is to consider both the total momentum (product of mass and velocity) and total kinetic energy (one half of mass and velocity squared). For a very bouncy collision, both momentum and kinetic energy should be conserved. It's very straightforward to mathematically solve for the ratio of masses such that one of the balls stops.
