A 60 g bullet fired from a 5 kg gun leaves with a speed of 500 m/s. Find the speed (velocity) with which the gun recoils (jerks backwards).

Applying conservation of momentum, we can write here,

Momentum before the bullet leaves the gun = Momentum after the bullet leaves the gun

Mass of the gun = 5 kg

Mass of the bullet = 60 g

The initial velocity of the gun = Initial velocity of the bullet = 0

The final velocity of the bullet = 500 m/s

The initial momentum of the system = Final momentum of the system

0 + 0 = 60 $\times$ 10^-3 kg $\times$ 500 m/s + 5kg $\times$ velocity of the gun

The velocity of the gun = $-\frac{30}{5}=-6\mathrm{m}/\mathrm{s}$

Hence, the recoil velocity of the gun is 6 m/s.