Question

Name the principle on which a rocket works?

Answer 1

Hint: A rocket is an aircraft, or spacecraft, or any other vehicle that obtains thrust from the rocket engine. It initially works against the gravitational force. And as the rocket moves in space the apparent weight of the rocket changes according to its distance from the earth and orientation.

Complete answer:
The rocket works on the principle of conservation of momentum. According to the conservation of momentum within a problem domain, the moment of the body always remains the same (constant).
Mathematically,
$\begin{align}
  & {{P}_{i}}-{{P}_{f}}=0 \\
 & \therefore {{P}_{i}}={{P}_{f}}\quad \cdots \cdots (1) \\
\end{align}$
Where,
${{P}_{i}}$ Is the initial momentum
${{P}_{f}}$ Is the final momentum
Energy moving objects in this universe have some momentum. Momentum is defined as the product of the mass of the body and the velocity with which it is moving. It is a vector quantity. A vector quantity has magnitude as well as direction. It is denoted by $P$.
Mathematically,
$P=m\times v$

Additional information:
The force acting on the moving body can be defined as the rate of change of momentum carried by the body.
Mathematically,
$F=\dfrac{dP}{dt}$
This can be further simplified as,
$\begin{align}
  & F=m\dfrac{dv}{dt} \\
 & \Rightarrow F=ma\quad ....(2) \\
\end{align}$
Equation (2) is known as Newton’s ${{2}^{nd}}$ Law of motion.
Thus, the rockets work on the principle of conservation of momentum. And this is the required answer to the question.

Note:
The engine of the rocket works with the use of ${{3}^{rd}}$ the law of motion (action and reaction). It simply pushes the rocket forward by expelling the engine exhaust in the opposite direction (initially towards the ground) at a very high speed. With this, it can also work in a vacuum of space.