Law of Conservation of Linear Momentum:

If no external force acts on a system (isolated), the total momentum of the system remains constant with time.

• If then constant
• This Law us is independent of frame of reference though linear momentum depends on frame of reference.

Practical applications of the law of conservation of linear momentum

(i) When a man jumps out of a boat on the shore, the boat is pushed slightly away from the shore.

(ii) A person left on a frictionless surface can get away from it by blowing air out of his mouth or by throwing some object in a direction opposite to the direction in which he wants to move.

(iii) Recoiling of a gun : For bullet and gun system, the force exerted by trigger will be internal so the momentum of the system remains unaffected.

Let m_G = mass of gun, m_B = mass of bullet,

v_G = velocity of gun, v_B = velocity of bullet

Initial momentum of system = 0

Final momentum of system

By the law of conservation linear momentum

So recoil velocity

Question: Why It is easier to pull than to push.

Answer:

When a pull is acting at an angle (θ) to the horizontal (upward)

R + F sin θ = mg

Applying Equation Along X Axis

R-mg+Fsin θ  =0

Þ          R = mg – F sin θ

and       F cos θ = ma

therefore

When a push is acting at an angle (θ) to the horizontal (downward)

R = mg + F sin θ

and       F cos θ = ma