A ball with a mass of # 5 kg# is rolling at #12 m/s# and elastically collides with a resting ball with a mass of #4 kg#. What are the post-collision velocities of the balls?
The velocities are
Here it's an elastic collision with no loss of kinetic energy.
We have the conservation of momentum.
There is also conservation of kinetic energies
Plugging this value in