Problem 64 - A Complete Resource Book in Chemistry for JEE Main

Question

Thrust imparted to the rocket is governed by the (a) gravitational law (b) third law of thermodynamics (c) Newton's third law (d) none of the above

Step-by-Step Solution

Answer

(c) Newton's third law.

Step 1: Understand the Concept of Thrust

Thrust in rocketry is a force that moves the rocket forward, which results from expelling gas out of the rocket's engine at high speed.

Step 2: Recognize the Related Physics Law

The underlying physics principle explaining the movement and thrust of rockets is Newton's Third Law of Motion. This law states that for every action, there is an equal and opposite reaction.

Step 3: Apply the Law to the Problem

When a rocket expels gases out of its nozzle, it is an action force. According to Newton's third law, the reaction force propels the rocket forward, providing thrust.

Step 4: Identify the Correct Choice

Among the options given, the principle governing thrust in rockets as per our discussion (Newton's Third Law of Motion) corresponds to option (c).

Key Concepts

Thrust in rocketry

Thrust is a fundamental concept in rocketry, pivotal in understanding how rockets launch and propel into space. When a rocket engine fires, it expels gas at high speed in the opposite direction the rocket intends to travel. This expulsion generates a reactive force known as thrust, which pushes the rocket forward. The magnitude of thrust depends on two factors: the speed at which the gas is expelled and the mass of the gas being ejected.
One of the most important aspects of thrust is ensuring that it is greater than the gravitational forces acting upon the rocket. For a successful launch, the thrust must exceed the gravitational pull of Earth. This requirement means engineers and scientists must meticulously calculate and optimize rocket engines to produce enough thrust during different stages of flight.
The concept of thrust also involves understanding nozzle design, combustion chamber efficiency, and fuel selection, all aimed at maximizing the force that actions the rocket upward.

Physics laws of motion

Newton's laws of motion form the backbone of classical mechanics and are crucial for analyzing how rockets operate. These laws explain the fundamental principles governing motion and force interactions on an object, like a rocket.
1. **Newton's First Law (Law of Inertia)**

• States that an object will remain at rest or in uniform motion unless acted upon by an external force.
• This law implies a rocket on the launch pad will not move until the engines provide thrust.

2. **Newton's Second Law (F = ma)**

• States that the acceleration of an object depends on the net force acting upon it and its mass.
• This law is used in calculating the required force (thrust) to accelerate the rocket to overcome inertia and gravity.

3. **Newton's Third Law (Action and Reaction)**

• This is particularly relevant to rocketry as it explains that every action has an equal and opposite reaction.
• When gases are expelled from the rocket, the rocket experiences an equal and opposite force (thrust) moving it forward.

The combination of these laws allows engineers to design rockets that successfully launch, reach their intended orbit, and return when necessary.

Rocket propulsion concepts

Understanding rocket propulsion requires a grasp of how propulsion systems convert energy into thrust to move rockets. This process begins in the combustion chamber, where fuel and oxidizer ignite to create high-pressure, high-temperature gas.
**Types of Rocket Propulsion:**

• **Chemical Propulsion:** The most common form, where chemical reactions produce gases expelled at high speeds to create thrust. It includes liquid and solid propellant rockets.
• **Electric Propulsion:** Utilizes electromagnetic fields and is typically used in deep space missions due to higher efficiency but lower thrust.
• **Nuclear Propulsion:** Still largely theoretical, it involves nuclear reactions to heat gases for expulsion, promising significant advancements in thrust capability.

In these propulsion systems, the nozzle plays a critical role in directing the flow of exhaust gases, optimizing thrust and controlling the vehicle's trajectory.
Ultimately, mastering rocket propulsion involves balancing the propulsion type, fuel efficiency, thrust production, and the mission's demands to achieve successful space travel.