Question

A ball with a mass of `1` `kg` moving at `6` `ms^-1` hits a still ball with a mass of `4` `kg`. If the first ball stops moving, how fast is the second ball moving?

Answer 1

Momentum, `p=mv`, is conserved. A stationary ball has no momentum, so all of the momentum is transferred from the first ball to the second. Before the collision, `p=mv=1xx6=6` `kgms^-1`. After the collision, `v=p/m=6/4=1.5` `ms^-1`.