# Question #ea570

Jan 15, 2018

Suppose, you had a rifle of mass $M$ and bullet of $m$ in it,now after firing the bullet goes away from the rifle with a velocity of $u$,if you consider that the velocity of rifle due to this process will be $v$ then we can use the law of conservation of momentum as no external force is acting on the system.

so,we can write,
$M \cdot 0 + m \cdot 0 = M \cdot v + m \cdot u$

or, $v = - \left(\frac{m}{M}\right) \cdot u$

negative sign means the rifle will move in the opposite direction of the bullet, and as $m$ is << than $M$ so from this equation we can say, $v$ will also be << than $u$ i.e the velocity of rifle will be very small than that of bullet.

so,that's how their mass affected their velocities.

But as the bullet will go through air before hitting something it's retardation will occur based on air resistance.

Whereas the rifle will move very little and almost no acceleration because it's so heavy.