Question

A bullet of mass 15 g is horizontally fired with a velocity 100 ms -1 from a pistol
of mass 2 kg. What is the recoil velocity of the pistol?

Answer 1

Explanation:

Since you didn’t specify whether we’re dealing with any external interactions, I assume the action takes places inside a closed system.

Here one can use the principle of conservation of momentum.

pi (initial momentum) =pf (final momentum)

Momentum is equal to mass multiplied by velocity. The wooden block is in a state of rest, hence one needs not to include it into the equations.

pi=mbullet⋅vbullet

Since the bullet imbeds into the wooden block, they share the same final velocity; thus the final momentum is equal to the sum of the two masses multiplied by the final velocity.

pf=(mbullet+mblock)⋅vf

Solving for vf gives us the following equation.

vf=mbullet⋅vbulletmbullet+mblock

Plugging in the given data yields us the final speed of 4.0 m/s , given one preserves the two significant figures.