Let there be two bodies of mass M and m, let the body M be moving with velocity V and the body m be at rest.
Now when the body (M) will collide with the body (m) the KE would be conserved hence the body M will come to rest and body m will move with velocity V.
Putting the value of variables in the equation below;
where V is velocity of separation of body M ,
v is velocity of separation of body m,
U is velocity of approach of body M,
u is velocity of approach of body m.