Question

Two objects collide and bounce apart. Assuming no outside forces act on the system, which best describes the total momentum after the collision?

It is always greater than it was before the collision.
It is often greater than it was before the collision.
It is always the same as it was before the collision.
It is often the same as it was before the collision.

Answer 1

It is always the same as it was before the collision.

Reason: with no external forces the total momentum of an isolated system is conserved, so the vector sum m1v1 + m2v2 before equals that after the collision (though individual momenta and kinetic energy can change).