Question

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

• A. One
• B. Four
• C. Two
• D. Three

Answer 1

Answer: (D)

$u=$ velocity of bullet
$\frac{dm}{dt}=$ Mass fired per second by the gun
$\frac{dm}{dt}=$ Mass of bullet $\left(m_B\right)\times$ Bullets fired per sec $(N)$
Maximum force that man can exert $F=u\left(\frac{dm}{dt}\right)$
$\therefore F=u\times m_B\times N$
$\Rightarrow N=\frac{F}{m_B\times u}$
$=\frac{144}{40\times 10^{-3}\times 1200}$
$=3$