M v the momentum of the object. Momentum is a vector, it has magnitude and direction, it points in the same direction as the velocity. The quantity force times time F t is called the impulse. An impulse changes momentum. If F is the total or net force, then it is called the total or net impulse.
Impulse is a vector also, in the direction of the force.
This will equal the change in momentum of the 5kg mass. If the net impulse is 0, the momentum will not change. It has to do with impulse. If we have a certain momentum, it will take an impulse of equal magnitude and opposite direction to stop us. If we stop quickly, the time is short, or small, and the force must be large.