IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

# Newton's Third Law and Rocket

## Introduction

The rocket works on the principle of Newton's third law. In this experiment, we measure the thrust (force) produced by the rocket.

## Apparatus

Diwali rocket, weighing balance, stand, matchbox

## Procedure

Take a rocket used in Diwali. Make sure that this is of type that do not explode (produce sound) when it goes up. Remove the stick from the rocket. Take a container (a bowl etc.) and fill it with sand. Insert the rocket in sand (upside down) such that only a small part remains outside the sand. Put the container on pan-balance (preferably having a range of 250 gram). Now, ignite the rocket and see how the needle of pan balance fluctuate. You can note down the reading and find the force produced by the rocket.

## Discussion

The gases coming out of the rocket produce a reaction force on the rocket. This force is transmitted to the pan-balance and is measured by it.

Generally, rocket produce a force of approximately $$F=mg=50\times{10}^{-3}\times 10\approx 0.5\,\mathrm{N}$$.

## Note

Hazard: Be careful while handling the rocket. Do this experiment in open (not within the room) as rocket produce lot's of smoke.