Physics 100-Level Past Questions.

Introduction

Good day, students!
Welcome to this detailed physics tutorial where we explore 100-level university physics past questions, compiled from the University of Abuja and the Federal University of Technology, Akure (FUTA).

In this session, we will focus on the Law of Conservation of Linear Momentum and how it relates to rocket propulsion — a key topic in mechanics and motion. This topic is essential for undergraduate physics students and those preparing for engineering entrance exams.

You can watch the full class in the video below:

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https://www.youtube.com/watch?v=CdrXFpVyLEI&t=15s

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Question 1: State and Explain the Law of Conservation of Linear Momentum

Question:
State and explain the law of conservation of linear momentum. Use it to derive the principle of rocket propulsion.

Definition of Linear Momentum

Linear momentum (p) is defined as the product of mass (m) and velocity (v) of an object: p=mvp = mvp=mv

The Law of Conservation of Linear Momentum states that:

In a closed system of particles (where no external force acts), the total momentum before an interaction is equal to the total momentum after the interaction.

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Real-Life Application: Rocket and Jet Propulsion

Let’s relate this principle to rocket propulsion:

• When a rocket launches from Earth, it expels gas backward at high speed.
• According to Newton’s Third Law and momentum conservation, the rocket moves forward in the opposite direction.

Imagine this:

• If the rocket is moving right,
• The exhaust gas is expelled left.

The momentum of the gas and the rocket remain equal and opposite, ensuring the total system momentum stays constant.

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Mathematical Representation:

Let:

• M be the mass of the rocket before expelling gas
• v be the velocity of the rocket
• m be the mass of expelled gas
• u be the velocity of the gas

Watch more educational videos and past questions: https://youtube.com/@allcbts

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Key Insights

• Rocket propulsion relies on the reaction from gas ejection.
• The system’s total momentum remains conserved at every point.
• This principle explains the backward thrust that accelerates rockets forward in space.

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