If the force on a rocket having an exhaust velocity of $300 \, m/s$ is $210 \, N$,then the rate of combustion of the fuel is ........... $kg/s$.

$A$ block of metal weighing $2 \,kg$ is resting on a frictionless plane (as shown in figure). It is struck by a jet releasing water at a rate of $1 \,kg \,s^{-1}$ and at a speed of $10 \,m \,s^{-1}$. Then,the initial acceleration of the block,in $m \,s^{-2}$,will be:

$A$ rocket of mass $5700 \,kg$ ejects mass at a constant rate of $15 \,kg/s$ with a constant speed of $12 \,km/s$. The acceleration of the rocket $1 \,minute$ after the blast is ........... $m/s^2$ $(g=10 \,m/s^2)$.

$A$ rocket with a lift-off mass $2 \times 10^4\,kg$ is blasted upwards with an initial acceleration of $5\,m\,s^{-2}$. The initial thrust of the blast is (Take $g = 10\,m\,s^{-2}$).

$A$ train is moving with a velocity of $20 \, m/s$. Dust is falling on it at the rate of $50 \, kg/min$. The extra force required to move this train with a constant velocity will be ....... $N$.

$Assertion$ : $A$ rocket moves forward by pushing the surrounding air backwards.
$Reason$ : It derives the necessary thrust to move forward according to Newton's third law of motion.