$A$ rocket of initial mass $1500 \ kg$ ejects gas at a constant rate of $10 \ kg/s$ with a relative speed of $5 \ km/s$. What is the acceleration of the rocket $50 \ s$ after the launch,neglecting gravity (in $m/s^2$)?

$A$ metal block of $2 \,kg$ is at rest on a smooth plane. It is struck by a water jet releasing water at a rate of $1 \,kg \,s^{-1}$ with a speed of $5 \,ms^{-1}$. The acceleration of the block is: (in $\,ms^{-2}$)

$A$ rocket has an initial mass of $20 \times 10^3 \, kg$. If it is to blast off with an initial acceleration of $4 \, m/s^2$,the initial thrust needed is $(g = 10 \, m/s^2)$.

$A$ block of metal weighing $2 \, kg$ is resting on a frictionless plane. It is struck by a jet releasing water at a rate of $1 \, kg/s$ and at a speed of $5 \, m/s$. The initial acceleration of the block will be .......... $m/s^2$.

$A$ rifle of $20 \,kg$ mass can fire $4$ bullets per second. The mass of each bullet is $35 \times 10^{-3} \,kg$ and its final velocity is $400 \,ms^{-1}$. What force must be applied on the rifle so that it does not move backwards while firing the bullets (in $\,N$)?

The motion of a rocket in an upward direction with high speed is based on the principle of conservation of: