This is the law of conservation of momentum. It is true for all collisions. Watch this video for a practical demonstration of conservation of momentum in elastic collisions.

we differentiate between elastic and inelastic collisions. The conservation of momentum and the conservation of energy are explored as we do examples involving these two types of collisions.

the momentum after the collision is zero. In physics, this type of event is termed an explosion. Watch this video for a practical demonstration of conservation of momentum in explosions.