Answer: C. It is always the same as it was before the collision.
Explanation:
The momentum, p, of an object is defined as the product of its mass, m, and its velocity, v: p = mv
The law of momentum conservation states that when there are no outside forces the total momentum of the system must be conserved.
Hence, when two objects collide and bounce apart, and no outside forces act on the system, the total momentum after the collision is always the same as it was before the collision.
This is a very important fact which permits you to deal with collision problems.
There are two types of collisions: inelastic collisions and ellastic collisions. While in elastic collisions you can use the conservation of mechanical energy to solve the problems, in inelastic collisions there is transformation of energy due to collision which implies that the mechanical energy is not conserved. Neverthelss, in both elastic and inelastic collisions, total momentum is conserved (it is the same after as it was before the collision), as long as no outside forces act on the system.
