Question

A ball A of mass 3kg and ball B of mass 4 kg are moving along the same straight line with speeds 7m/s and 5m/s respectively. They approach each other and collide. What is the speed of B after collision, if coefficient of restitution is 3/4?

Answer 1

Let the speeds of 3kg and 4 kg balls be v1 and v2 respectively.
So, by conservation of linear momentum

3(7)+4(5) = 3v1 + 4v2
3v1 + 4v2 = 41.........(1)

Now,
3/4 = v2-v1 / 7-5
v2 - v1 = 3/2.....(2)

Solve, equation 1 and 2 and you'll get the answer for v1 and v2.