A bullet, of mass 40 g is horizontally fired with a velocity 150 ms-1 from a pistol of mass 3 kg. What is the recoil velocity of the pistol?

A bullet, of mass 40 g is horizontally fired with a velocity 150 ms-1 from a pistol of mass 3 kg. What is the recoil velocity of the pistol? Correct Answer - 2.0 ms^-1

The correct answer is option 4, i.e., - 2.0 ms-1.

• The recoil velocity is the velocity by which pistol bounces back when a bullet is fired.
• In this case, the momentum of the bullet is equal to the momentum of the pistol.
• Hence, m_bv_b = m_pv_p (where m_b and m_p are the masses of bullet and pistol respectively and v_b and v_p are the velocities of bullet and pistol respectively).
• 3 x v_p = 40 x 10^-3 x 150
• v_p = 40 x 10-3 x 50 
• v_p = 2000 x 10-3 
• v_p = 2 m/s
• Here, the velocity of pistol is taken with negative sign because, it is in the opposite direction to that of the velocity of the bullet, i.e., bullet moves forward and pistol moves backwards.