Question

What will be momentum of a 3 kg gun, if a 10 g bullet accelerates to 350 m/s, after being fired from the gun.

• A. 3500 kg-m/s, forward
• B. 3500 kg-m/s, backward
• C. 3.5 kg-m/s, forward
• D. 3.5 kg-m/s, backward

Answer 1

The correct option is D 3.5 kg-m/s, backward

The momentum of bullet:
$p_b=mv$
$p_b=\left(10/1000kg\right)\times 350m/s$
$p_b=3.5kgm/s$

Gun recoils in direction opposite to the bullet, by Newton’s third law.

By applying to law of conservation of momentum, the gun will possess a momentum of $-3.5kgm/s$. Negative sign shows that the momentum will be opposite to that of bullet, which means it is in the backward direction.