A ball with a mass of # 2 kg# is rolling at #5 m/s# and elastically collides with a resting ball with a mass of #9 kg#. What are the post-collision velocities of the balls?
If post collision velocities be u m/s for 1st one and v m/s for 2nd one ,then applying conservation of momentum
Now collision being elastic KE will be conserved and consequently the relative velocity of 1st object with respect to 2nd is reversed .
Comparing (1) and (2)