Momentum
Momentum of a body is the quantity of motion possessed by the body. It is equal to the product of mass and velocity of the body.
Momentum = Mass × velocity = mv
Momentum is a vector quantity because the velocity is a vector and mass m is a scalar. Its direction is same as the direction of the velocity of the body. Its magnitude is given by
p = m v
SI unit of momentum = kg ms-1
CGS unit of momentum = g cm s-1.
The dimensional formula of momentum is [MLT-1].
Newton’s Second Law of Motion:
The rate of change of linear momentum of a body is directly proportional to the applied force and the change takes place in the direction of the applied force.
F = dp/dt
Numerical Problems Based on Class 11 Physics Linear Momentum and Force
Q.1. A truck starts from rest and rolls down a hill with constant acceleration. It travels a distance of 400 m in 20 s. Calculate the acceleration and the force acting on it if its mass is 7 metric tonnes.
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Answer: 2 ms-2,14,000 NQ.2. A balloon has a mass of 5 g in air. The air escapes from the balloon at a uniform rate with a velocity of 5 cms-1. If the balloon shrinks completely in 2.5 s, find the average force acting on the balloon.
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Answer: 10 dyneQ.3. A motor car running at the rate of 7 ms-1 can be stopped by applying brakes in 10 m. Show that total resistance to the motion, when brakes are on, is one fourth of the weight of the car.
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Answer:Q.4. A force acts for 10 s on a body of mass 10 kg after which the force ceases and the body describes 50 m in the next 5 s. Find the magnitude of the force.
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Answer: 10 NQ.5. A force of 50 N is inclined to the vertical at an angle of 30°. Find the acceleration it produces in a body of mass 2 kg which moves in the horizontal direction.
