A body of mass 18 kg moving with velocity 4 m s−1 collides with another body of mass 6 kg moving in the opposite direction with velocity 10 m s−1. If they stick together after collision, find their common velocity.
Worked solution (try it first)
Take the direction of the 18 kg body as positive.
The total momentum before is 18(4)+6(−10)=72−60=12 kg m/s.
Momentum is conserved and the bodies move together with mass 18+6=24 kg, so 24v=12.