Two balls are moving towards each other on a vertical line collides with each other as shown. Find their velocities just after collision.

Explanation

Let the final velocity of 4 kg ball just after collision be v. Since, external force is gravitational which is non - impulsive, hence, linear momentum will be conserved.
Applying linear momentum conservation:

`2(-3)+4(4)=2(4)+4(v)`
or `v=(1)/(2)m//s`