A bullet of mass 60 g is fired with a velocity of 60 m/s from a gun of mass 10 kg. Calculate the recoil velocity of the gun.

As no external force is acting on the bullet-gun system, the momentum of the system will remain conserved.
Let $m_1=$ Mass of the bullet = 60 g = 0.06 kg
$m_2=$ Mass of the gun = 10 kg
$v_1$ = Velocity of the bullet = 60 m/s
$v_2$ = Recoil velocity of the gun
Applying the conservation of momentum, $m_1{v}_1=m_2{v}_2$
$\Rightarrow 0.06\times 60=10\times v_2$
$\Rightarrow v_2=0.36m/s$