Momentum: All moving objects have momentum. If an object is not moving, the momentum is zero.

Formula

Where $p$ is the momentum in kilograms meters per second $kgms^-1$, $m$ is the mass in kilograms (kg), and ($v$) is the velocity in meters per second $ms^-1$.

Remember, momentum is a vector.

Force is equal to the rate of change of momentum.

Where $F$ is the force, $mv$ is the final momentum, $mu$ is the initial momentum, and $t$ is the time.

In a closed system, the total momentum before an event is equal to the total momentum after the event. This principle is known as the conservation of momentum.

After the collision, the total momentum remains $mv.$ Ball B, which was initially stationary, now has velocity and momentum, while ball A moves with a reduced velocity. The sum of these two momentums after the collision will still equal the total momentum before the collision, $mv.$