**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 Ã— 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.

**Show Answer**

Answer: 2 ms^{-2},14,000 N

Q.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.

**Show Answer**

Answer: 10 dyne
Q.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.

**Show Answer**

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.

**Show Answer**

Answer: 10 N
Q.5. A force of 50 N is inclined to the vertical at an angle of 30Â°. Find the acceleration it produces in a body of mass 2 kg which moves in the horizontal direction.

**Show Answer**

Answer: 12.5 ms^{-2}