A machine gun fires a bullet of mass $40 g$ with a velocity $1200 m{s}^{–1}$ . The man holding it, can exert a maximum force of $144 N$ on the gun. How may bullets can he fire per second at the most ?

The force exerted by machine gun on man's hand firing a bullet

$=$ change in momentum per second on a bullet or rate of change of momentum

$=\left(\frac{40}{1000}\right)\times 1200=48N$

The force exerted by man on machine gun $= 144 N$

Hence, number of bullets fired

$=\frac{144}{48}=3$