A bullet of mass 10 g is horizontally fired with velocity 300 m s^-1 from a pistol of mass 1 kg. What is the recoil velocity of the pistol?

Concept:

• The momentum of a body is the product of the mass of the body and the velocity of the body. It is a vector quantity, so it possesses both magnitude and direction.
• Principle of conservation of linear momentum - Linear momentum of a system remains constant (in magnitude and direction) if the external forces acting on the system add up to zero.

m₁v₁ + m₂v₂ = 0 -- (1)

Calculation:

Given: mass of bullet m₁ = 10 g, velocity of bullet v₁ = 300 m s^-1,

mass of pistol m₂ = 1 kg = 1000 g

Now from equation 1,

10 g × 300 m s^-1 + 1000 g × v₂ = 0

⇒ v₂ = -3 m s^-1

We know that gun always recoils backward so, 

V2 = - (-3 m/s)

= 3 m/s