A bullet, of mass 20 g, is horizontally fired with a velocity 150 ms-1 from a pistol of mass 2.5 kg. What is the recoil velocity of the pistol?

A bullet, of mass 20 g, is horizontally fired with a velocity 150 ms-1 from a pistol of mass 2.5 kg. What is the recoil velocity of the pistol? Correct Answer -1.2 ms^-1

The Correct Answer is Option 3 i.e -1.2 ms-1.

• Mass of bullet, M = 20g = 0.02 kg
• Mass of pistol, m = 2.5 kg
• Initial velocity of the bullet (u₁) and pistol (u₂) = 0
• Final velocity of the bullet, v₁ = 150 ms^-1.
• Let V be the recoil velocity of the pistol.
• The total momentum of the pistol and bullet before the fire is zero. (Since both are at rest i.e u₁ and u₂ is zero)
• The total momentum of the pistol and bullet after it is fired is
• = (0.02 x 150 ) + (2.5 x V) = (3 + 2.5V) kg ms^-1.
• Total momentum after the fire = Total momentum before the fire 
• 3 + 2.5V = 0
• V = -1.2 m/s  
• Therefore, the recoil velocity of the pistol is -1.2 ms^-1.