Question

A rocket works on the principle of
(a). Conservation of mass
(b). Conservation of energy
(c). Conservation of linear momentum
(d). None of these

Answer 1

- Hint: Forward motion of rocket is due to the thrust developed by the ejaculation of fuel gases in the backward direction. This will provide momentum for the take off.

Complete step-by-step solution -

In a rocket, a large amount of fuel is used to produce a large impact. It burns at high temperature. Due to the burning the gases will come out through a nozzle at the back of the rocket. This ejecting gas exerts momentum and forward motion to the rocket. When more gases are coming out the acceleration also increases accordingly. Since the nozzle is very small, the mass of gases escaping per second is also small. So that it will provide an effective velocity to the rocket. This is actually providing equal and opposite momentum to the rocket. Thus, the rocket works on the principle of conservation of linear momentum. Hence the option (c) is correct.
Additional information: All rockets, jet engines and some balloons are working with this principle and this is extensively used for the study of astronomy and space science. Recoil of gun is also an example for this concept.

Note: It is an extension of Newton’s third law of motion. The gases forcefully ejected from the rocket produce equal and opposite momentum, thus it will move towards the sky. Do not make any concepts regarding the conservation of energy for the rocket propulsion. It is completely conservation of momentum.