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Question: Answered & Verified by Expert
A bullet of mass $m$ is fired from a rifle of mass $M$. If $\mathbf{v}$ be the velocity of the bullet, velocity acquired by the rifle is
PhysicsCenter of Mass Momentum and CollisionAP EAMCETAP EAMCET 2021 (24 Aug Shift 2)
Options:
  • A $\mathbf{v}_r=\frac{-M}{m} \mathbf{v}$
  • B $\mathbf{v}_r=\frac{-m}{M} \mathbf{v}$
  • C $\mathbf{v}_r=-\mathbf{v}$
  • D $\mathbf{v}_r=+\mathbf{v}$
Solution:
2532 Upvotes Verified Answer
The correct answer is: $\mathbf{v}_r=\frac{-m}{M} \mathbf{v}$
Given that, mass of bullet $=m$
Mass of rifle $=M$
Velocity of bullet $=\mathbf{v}$
Let velocity of rifle $=\mathbf{v}_r$
By using conservation of linear momentum
$m \mathbf{v}+M \mathbf{v}_r=0$ $[\because$ Initial momentum of bullet and rifle was zero]
$\therefore \quad \mathbf{v}_r=\frac{-m \mathbf{v}}{M}$
Here - ve sign shows that velocity of rifle is opposite to the velocity of bullet.

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