Question

Explain the principle of conservation of momentum with an example of bullet and riffle

Answer 1

law of conservation of momentum states that:”The momentum of an isolated system of two or more than two interacting bodies remains constant.”Momentum of a system depends on its mass and velocity.A system is a group of bodies within certain boundaries .An isolated system is a group of interacting bodies on which no external force is acting.
 A system of gun and a bullet.Before firing the gun,both the gun and the bullet are at rest,so the total momentum of the system is zero.As the gun is fired,bullet shoots out of the gun and acquires momentum.To conserve momentum of the system,the gun recoils.According to the law of conservation of momentum,the total momentum of the gun and the bullet will be zero after the gun is fired.Let m be the mass of the bullet and v be thevelocity on firing the gun; M be the mass of the gun and V be the velocitywith which it recoils.Thus the total momentum of the gun and the bullet after the gun is fired will be:

Total momentum of gun and bullet after the gun is fired = M v + m v ….(1)

According to the law of conservation of momentum:

Total momentum of gun and bullet after the gun is fired =Total momentum of gun and bullet before the gun is fired

Therefore we get:

M V +mv = 0

or M V = -m v

Hence:



Above equation gives the velocity V of the gun, negative sign indicates that velocity of the gun is opposite to the velocity of the bullet. i .e the gun recoils.Since  mass of the gun is much larger than the bullet,therefore, the recoil is much smaller then the velocity of the bullet.