Principle of Conservation of Linear Momentum


 
 
Concept Explanation
 

Principle of Conservation of Linear Momentum

The linear momentum of a particle is defined as the product of the mass and velocity of that particle. Conservation of momentum of a particle is a property exhibited by any particle where the total amount of momentum never changes. Linear momentum of a particle is a vector quantity and is denoted by underset{p}{rightarrow}

If the net external force on a system of particles is zero, the linear momentum of the system remains constant.

Explanation:

This means that internal forces cannot change the linear momentum of the system. Internal forces can change the momenta of the different particles in the system. If the momentum of one particle is increased, that of some other particle must decrease to keep the total momentum of the system constant.

Q. Two particles A and B of masses 20g and 30g respectively are at rest  at a certain time.Because of the force exerted  by them on each other, the particles start moving. At a given instant ,particle A is found to move towards the east with a velocity of 6cm/s. What is the velocity of particle B at this instant?

Solution: As the particles are at rest initially, the linear momentum of each is zero.The force exerted by the particles on each other are internal forces of the system and cannot change the linear momentum of the system, which remains zero during this time.

At the given instant,the linear momentum of particle A is 

                           p_1:=:m_1v_1:=:(20g)(6cm/s):=:120 :g;cm/s

The linear momentum of particle B at this must be -120 g cm/s to make the momentum of the system zero. Thus, particle B moves towards the west with a velocity v_2, where 

          m_2v_2:=:120:g:cm/s

          v_2;=;frac{120:g:cm/s}{m_2}:Rightarrow :frac{120:g:cm/s}{30:g}:=;4:cm/s

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

A bullet of mass 20 g is fired from a gun of mass 5 kg with a velocity of 150 ms^-^1. The recoil velocity of the gun is :

Right Option : B
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Explanation
Question : 2

What is the motion of the rocket based on ?

 

 

Right Option : B
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Explanation
Question : 3

A bullet of mass 50g is horizontally fired with a velocity of 130 ms^-^1 from a gun of mass 5 kg. What is the recoll velocity of the gun?

Right Option : A
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Explanation
 
 


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