Mass of Each bullet, $\left(m\right)=1\mathrm{ g}=0.001 \mathrm{kg}.$

Velocity of bullet, $\left(v\right)=10 \mathrm{m }{\mathrm{s}}^{-1}$

Applied force, $\left(F\right)=5\mathrm{ <mn> g</mn><mn> w</mn><mn>t</mn>}$

$=\frac{5}{1000}\times 10=0.05\mathrm{ N}.$

Let $n$ bullets are fired per second, then

Force = rate of change of linear momentum

i.e., $F=n\times mv$

$\therefore$ Number of bullets fired per second,

$n=\frac{F}{mv}=\frac{0.05}{0.001\times 10}=5$