PART–2 : Exam Essay-Type Questions & Answers
These questions are framed according to Intermediate Board Examinations and also help in building strong fundamentals for IIT–JEE.
Question 1 (8 Marks)
State and explain Newton’s First Law of Motion. Illustrate with suitable examples.
Answer:
Newton’s First Law of Motion states that a body continues in its state of rest or uniform motion in a straight line unless acted upon by an external unbalanced force. This law is also known as the Law of Inertia.
According to this law, no force is required to maintain the motion of a body. Force is required only to change the state of motion of a body.
Explanation:
- If a body is at rest, it remains at rest unless an external force acts on it.
- If a body is moving with constant velocity, it continues to do so unless an external force acts.
Examples:
- Passengers fall backward when a bus starts suddenly.
- Passengers fall forward when a moving bus stops suddenly.
Thus, Newton’s First Law explains the property of inertia and the need for force to change motion.
Question 2 (10 Marks)
State and derive Newton’s Second Law of Motion. Hence define force.
Answer:
Newton’s Second Law of Motion states that the rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction of the force.
Derivation:
Let a body of mass m be moving with initial velocity u. After applying a force F, its velocity becomes v in time t.
Initial momentum = mu
Final momentum = mv
Change in momentum = mv − mu = m(v − u)
Rate of change of momentum = m(v − u)/t = ma
According to the law,
F ∝ ma
Introducing proportionality constant,
F = ma
Thus, force is defined as the product of mass and acceleration.
Question 3 (5 Marks)
Define momentum. Write its SI unit and dimensions.
Answer:
Momentum is defined as the product of mass and velocity of a body.
Momentum (p) = mv
SI unit of momentum is kg m s−1.
Dimensional formula of momentum is [MLT−1].
Question 4 (8 Marks)
State and explain Newton’s Third Law of Motion with examples.
Answer:
Newton’s Third Law of Motion states that for every action, there is an equal and opposite reaction.
Action and reaction forces act on different bodies, are equal in magnitude, and opposite in direction.
Examples:
- Walking: The foot pushes the ground backward, and the ground pushes the body forward.
- Swimming: Water is pushed backward, and the swimmer moves forward.
- Recoil of a gun when a bullet is fired.
Thus, motion is possible only due to mutual interaction of bodies.
Question 5 (10 Marks)
Explain inertia. Describe different types of inertia with examples.
Answer:
Inertia is the property of a body by virtue of which it resists any change in its state of rest or uniform motion.
Types of inertia:
- Inertia of Rest: Tendency to remain at rest.
- Inertia of Motion: Tendency to continue uniform motion.
- Inertia of Direction: Tendency to maintain direction of motion.
Examples:
Passengers experience jerks when a bus starts, stops, or turns suddenly.
Inertia depends on mass. Heavier bodies have greater inertia.
PART–2 Completed.
These answers are suitable for board exams and build a strong base for competitive exams.
📚 Physics Thinking Library – How IIT Toppers Think
Welcome to the Physics Thinking Library by Mind Grow Magazine. This library is specially designed for IIT–JEE & Intermediate students to understand how toppers think, decide, and solve Physics problems.
🎯 What You Will Learn From This Library
- How IIT toppers approach Physics questions
- Decision-making during problem solving
- Common traps & how to avoid them
- Exam-hall mindset and logic flow
- Step-by-step thinking framework
📘 Complete Series: How IIT Toppers Think (Part 1–25)
Click on any part below to start learning. It is recommended to read in order.
- Part 1 – Introduction to Topper Thinking
- Part 2 – Understanding the Problem Statement
- Part 3 – Visualization & Physical Sense
- Part 4 – Role of Acceleration & Forces
- Part 5 – Free Body Diagram Thinking
- Part 6 – Method Selection Strategy
- Part 7 – Avoiding Formula Traps
- Part 8 – System Approach Mindset
- Part 9 – Friction & Constraint Thinking
- Part 10 – Time vs Accuracy Balance
- Part 11 – Common Thinking Mistakes
- Part 12 – Decision Flow in Tough Problems
- Part 13 – Eliminating Wrong Options
- Part 14 – Handling Multi-Concept Questions
- Part 15 – Pressure Handling in Exam Hall
- Part 16 – Speed Building Without Guessing
- Part 17 – Extreme Case Thinking
- Part 18 – Logical Shortcuts vs Blind Tricks
- Part 19 – Advanced Reasoning Techniques
- Part 20 – Rank-Deciding Thought Patterns
- Part 21 – Physics Intuition Development
- Part 22 – Eliminating Panic in Tough Questions
- Part 23 – Last-Minute Thinking Strategy
- Part 24 – Mistake-Proof Problem Solving
- Part 25 – Final Topper Framework
🧠 How to Use This Library Effectively
- Read 1–2 parts daily
- Apply thinking to real Physics problems
- Revisit library before exams
- Use as a mindset guide, not memorization
This library is a long-term asset for serious Physics learners.
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