$A$ Diwali rocket is ejecting $0.05\, kg$ of gases per second at a velocity of $400\, m/s$. The accelerating force on the rocket is

$A$ rocket works on the principle of conservation of which of the following?

Is the formula $\vec{F} = m\vec{a}$ valid in all circumstances? Why?

$A$ metal block of mass $4 \ kg$ is at rest on a frictionless surface. It is struck by a jet of water releasing $2 \ kg \ s^{-1}$ at a speed of $10 \ m \ s^{-1}$. The acceleration of the block is (in $m \ s^{-2}$)

$A$ gun of mass $10 \, kg$ fires $4$ bullets per second. The mass of each bullet is $20 \, g$ and the velocity of the bullet when it leaves the gun is $300 \, m/s$. The force required to hold the gun while firing is (in $N$)

$A$ rocket can go vertically upwards in the Earth's atmosphere because