Question

Rocket works on the principle of conservation of ______.
A) Mass
B) Energy
C) Momentum
D) Velocity

Answer 1

Hint: Recall Newton’s laws of motion (Third law). Remember there is no external force acting on the rocket when the rocket is launched. Don’t confuse between Energy, momentum and force.

Complete step by step answer:
Newton’s third law states that, for every action there is an equal and opposite reaction. Consider the rocket and its launch pad to be a single system. Now in this system no external force is applied so the momentum of the system must be conserved.
Momentum is given as the product of mass and velocity
$\Rightarrow$\[p=mv\]
Where
$\Rightarrow$\[p\] Is the momentum
$\Rightarrow$\[m\] Is the mass of the object taken in consideration
$\Rightarrow$\[v\] Is the velocity of the object.
When a rocket is in the initial phase of it’s launch what happens is that when we accelerate a small amount of gas in one direction, it pushes back with an equal and opposite force, accelerating a much larger spaceship at a proportionately smaller rate.
The rocket gains momentum which is equal to the momentum of the gas expelled but in the opposite direction, the boosters begin to expel gases after the rocket has begun to travel and thus the rocket continues to gain momentum, so that they get faster and faster as long as the engine is operating.
It must be noted here that rocket boosters consume around \[11,000\] pounds of fuel per second. This is more than \[20\] lakh times the amount of fuel used by an average car. It must also be noted that rockets travel at a speed which is around \[7-8km/s\] .
All this is done conserving the momentum of the system.
Therefore the correct option is C

Note: When the rocket moves upwards its velocity increases but mass decreases. As momentum is a product of mass and velocity, the momentum of the rocket at any given instance is exactly the same as initial momentum. It is also clear from the definition of momentum that for a body at rest its momentum is zero. Since the velocity is zero.