Since momentum is conserved the total momentum before the crash = the total momentum after the crash.

The total momentum before is the momentum of A + the momentum of B

The total momentum after is the new momentum of A + the new momentum of B

We can represent this with the equation:

Explosions (Also seen in GCSE Physics 2)

We look at explosions in the same way as we look at collisions, the total momentum before is equal to the total momentum after. In explosions the total momentum before is zero. [à is positive]