Question

In a rocket, a large volume of gases produced by the combustion of fuel is
allowed to escape through its tail nozzle in the downward direction with the
tremendous speed and makes the rocket to move upward. Which principle is
followed in this take off of the rocket?

Answer 1

The principle of rocket propulsion works on the 'Newton's Third Law of Motion'. It states that, 'to every action, there is always an equal and opposite reaction'.

In the case of a rocket, the engine emits hot burning gases in the downward direction. These gases apply an equal and opposite reaction force to the rocket in the upward direction.

This is how a rocket is propelled.

The principle of conservation of momentum states that whenever two bodies collide or get separated, then their total momentum before collision or separation is equal to their total momentum after collision or separation.

Since the gases of the rocket and the rocket are stationery at the start, their total momentum is zero. After the gases start burning, the momentum imparted to the rocket is equal and opposite to that of the gases. Hence their total momentum is zero.