Linear Momentum


 
 
Concept Explanation
 

Linear Momentum

Momentum measures the quantity of motion possessed by a body. It is defined as the product of the mass of a body and its velocity. For a linear motion it is called the linear momentum of the body. It is the vector quantity which means that the body's momentum is always in the same direction as its velocity vector. It is a conserved quantity which means that the total momentum of the system is constant. If “m” is the mass and “v” be the velocity of a body at some instant, the linear momentum is given by the expression -

                                                  p:=:mtimes:v

Here, p = momentum,  v  =  velocity   and   m   =  mass

As momentum and velocity are the vector quantities therefore, they are denoted asunderset{p}{rightarrow} and underset{v}{rightarrow} respectively.

The SI unit of momentum is kg m/s

Examples:

1. A bullet fired at a wooden board can destroy it. But a small stone of the same mass as the bullet when thrown at the board will hardly cause any damage.Although their masses are the same, the high velocity of the bullet gives it a larger momentum, which causes the damage.

2.Consider, a truck and a rickshaw moving with the same velocities, heading towards each other and eventually ending up in a head on collision. The rickshaw could might get deformed to such an extend that it would be  difficult for us to make it, while truck might get some minor damages.This is because of the larger momentum of the truck.

IllustrationA ball with a 500g mass is thrown with a velocity of 72 km/h. What is the initial momentum?

Solution:  Given

 mass of the ball = 500g = 0.5 Kg and

velocity of the ball = 72 km/h  = 20 m/s

 Momentum of the ball 

 p:=:mv:=:frac{1}{2}:times20:=:10:kg:m/s     

Illustration: The linear momentum of a body is 40 kg m/s and the mass of the object is 5 kg. Determine the velocity of the object.

Solution: Given parameters are, 

m  =  5 kg    and 

p  =  40 kg m/s

Linear momentum formula is given by 

p:=:mv

v;=:frac{p}{m}Rightarrow frac{40}{5}Rightarrow 8:m/s

Sample Questions
(More Questions for each concept available in Login)
Question : 1

A body of mass 5 kg undergoes a change in speed from 30 to 40 m/s. Its momentum would increase by

Right Option : A
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Question : 2

A body, whose momentum is constant, must have constant-

Right Option : B
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Question : 3

A Body of mass 25Kg collides against a wall with velocity 12 m/s and rebounds with the same speed. the change in momentum is

Right Option : D
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