Question

If one ball with a momentum of 50 kg·m/s hits a ball at rest and no other forces are acting on either ball, what's the total momentum of both balls after the collision?

Answer 1

Total momentum of both balls = momentum of the moving ball + momentum of the ball at rest

Since the ball is at rest, the ball does not have any velocity, thus the momentum of the ball at rest = 0

Therefore total momentum of the ball = 50kgms^-1

Answer 2

Apply conservation of momentum,
\(P_i=P_f\)
momentum of 1st ball before collision=momentum of 1st ball after collision + momentum of 2nd ball after collision.