Question

If the force on a rocket which is ejecting gases with a relative velocity of 300 m/s, is 210 N. Then the rate of combustion of the fuel will be :

• A. 10.7 kg/sec
• B. 0.07 kg/sec
• C. 1.4 kg/sec
• D. 0.7 kg/sec

Answer 1

The correct option is D 0.7 kg/sec

$F=\frac{d}{dt}\left(mv\right)$
$F=v\frac{dm}{dt}$
$210=300\times \frac{dm}{dt}\Rightarrow \frac{dm}{dt}=0.7kg/s.$