Momentum – Force and Laws of Motion

What is Momentum

It is the quantity of motion of a moving body & may be defined as a product of mass and velocity. Its unit is ‘kilogram meter per second’ or kg m/s.

The Momentum of heavier objects will be higher than compared of lighter objects. Since momentum is a product of Mass and Velocity, we can change momentum by increasing the mass of an object

Example: If a cricketer catches a ball he moves his hand back while catching the ball. He does this to reduce the impact, due to the force of the ball on his hand. An object in motion has momentum.

Change in Momentum

Change in Momentum = Mass x Change in Velocity
Change in Momentum = Mass x (New Velocity – Old Velocity)
Change in Momentum = m x (v -u)
Rate of Change in Momentum = m x (v -u) /t
Rate of Change in Momentum = m x a [acceleration, a = (v -u) /t ]
Rate of Change in Momentum = Force

The momentum of the object at the start of the time interval is called the initial momentum and the momentum of the object at the end of the time interval is called the final momentum. The rate of change of momentum of an object is directly proportional to the applied force.

F ∝ V (Directly proportional to Velocity)
F ∝ m (Directly proportional to Mass)
F ∝ m x V (Directly proportional to the product of Mass & Velocity)

Both quantities are required for the force to be applied.

F ∝ P (momentum)

Momentum: Momentum is defined by a body as the product of its mass and velocity. It is a vector quantity with SI unit = kg.ms-1

Question. What is the p of a man of mass 75 kg when he walks with a uniform velocity of 2 m/s.

Question. An object’s momentum is 80 kg m/s and its mass is 16000 G. Find the object’s velocity. Solution. p = 80 kg m/s m = 16000gm = 16 kg p = mv 80 = 16 x v v = 80/16

Question. Calculate the momentum of the following An elephant of mass 2000 kg moving at 5 m/s. A bullet of mass 0.02 kg is moving at 400 m/s.

Question. What is the change in momentum of a car weighing 1500 kg when its speed increases from 36 km/hr to 72 km/hr uniformly. .

A large amount of force acting on an object for a short interval of time is called impulse or impulsive force. Numerically impulse is the product of force and time. An impulse of an object is equal to the change in momentum of the object.