The force required to stop a moving body depends upon its mass. Suppose two balls of same mass are moving with different velocities. Which ball will need more force to stop? The faster moving ball require more force to stop it. Thus, the force required to stop a body also depends upon its velocity.

The impact produced by the objects depends on their mass and velocity. These two quantities define a new quantity called momentum.

The momentum, p of a moving body is defined as the product of its mass, m and velocity, v.

p = mv

SI unit of momentum is kilogram-metre per second (kg m s–1). Momentum has both magnitude and direction. Its direction is same as that of velocity.

1. Two similar trucks are moving on a road with the same velocity. One of them is empty while the other one is loaded. Which of the two has more momentum?

As momentum is equal to mass × velocity. So the momentum of loaded truck (more mass) has more momentum.

2. If a body of mass 5 kg moves with a velocity of 10 ms–1, then what is the momentum of the body?

Momentum = m × v

= 5 kg × 10 ms–1

= 50 kg ms–1