A ball with a mass of # 5 kg# is rolling at #18 m/s# and elastically collides with a resting ball with a mass of #3 kg#. What are the post-collision velocities of the balls?
Mass of 1st ball
Mass of 2nd ball
Initial velocity of 1st ball
Initial velocity of 2nd ball
Let post collision velocity of 1st ball be
Again the collision being elastic one the relative velocity of one ball with respect to the other is reversed by the collision and we get
By  and  we get