Question

A 10 kg gun recoils with a speed of 0.1 m/s after it fires a 0.001 kg bullet. What is the speed of the bullet?

Answer 1

As we know that here gun + bullet system is isolated from all other external force system

so here the momentum of system is always conserved

so we will say

$m_1v_{1i} + m_2v_{2i} = m_1v_{1f} + m_2v_{2f}$

here we know that

$v_{1i} = v_{2i} = 0$

$m_1 = 10 kg$

$m_2 = 0.001kg$

$v_{1f} = 0.1 m/s$

now we will have

$0 + 0 = 10(0.1) + 0.001v_{2f}$

by solving above equation we will have

$v_{2f} = 1000 m/s$