\(\frac{{dm}}{{dt}} = \) Mass thrown per second by the machine gun
\(= \)Mass of bullet \(×\) Number of bullet fired per second
\( = 10\;g \times 10\;bullet/\sec \)\( = 100\;g/\sec \; = \;0.1\;kg/\sec \)
\(\therefore \) Thrust \( = \frac{{udm}}{{dt}} = 500 \times 0.1 = 50\;N\)
$[g = 10\, {m} / {s}^{2} ]$