PART–4 (v) : IIT / JEE Previous Year Questions – Set 5
This set strengthens understanding of free body diagrams, system approach, and non-obvious force directions, which are frequently tested in IIT–JEE.
PYQ–21 (IIT–JEE)
Question:
A block of mass m is placed on a smooth inclined plane. Find the normal reaction exerted by the plane on the block.
Method Selection:
Resolve forces perpendicular to the inclined plane.
Solution:
Component of weight perpendicular to plane = mg cosθ
Since there is no acceleration perpendicular to the plane:
N = mg cosθ
Examiner’s Intention:
To test correct resolution of forces and understanding of normal reaction.
Common Mistake:
Taking normal reaction as mg.
PYQ–22 (IIT–JEE)
Question:
Two blocks of masses m and 2m are connected by a light string and pulled by a force F on a smooth surface. Find the tension in the string.
Method Selection:
First find acceleration of the system, then analyze one block.
Solution:
Total mass = 3m ⇒ a = F / 3m
For block of mass m:
T = ma = m(F / 3m)
T = F / 3
Examiner’s Intention:
To check system approach followed by individual body analysis.
Common Mistake:
Trying to find tension directly without calculating acceleration.
PYQ–23 (IIT–JEE)
Question:
A body is acted upon by a constant force. Which of the following quantities must change?
A) Velocity only
B) Momentum only
C) Acceleration only
D) Momentum and velocity
Method Selection:
Use Newton’s Second Law conceptually.
Solution:
Constant force ⇒ constant acceleration
Acceleration changes velocity and momentum.
Correct option: D
Examiner’s Intention:
To test conceptual understanding beyond formulas.
Common Mistake:
Choosing acceleration alone without considering velocity change.
PYQ–24 (IIT–JEE)
Question:
A body is moving in a circular path with constant speed. Is Newton’s First Law violated? Explain.
Method Selection:
Analyze direction of velocity and acceleration.
Solution:
Though speed is constant, direction of velocity changes.
Hence, acceleration exists toward the center.
Therefore, a force (centripetal force) acts on the body.
Newton’s First Law is not violated.
Examiner’s Intention:
To test understanding of velocity as a vector.
Common Mistake:
Assuming no force because speed is constant.
PYQ–25 (IIT–JEE)
Question:
A block rests on a horizontal surface. Why does it not move even though gravitational force acts on it?
Method Selection:
Conceptual equilibrium analysis.
Solution:
Gravitational force mg is balanced by normal reaction N.
Net force is zero, hence no acceleration.
The block remains at rest.
Examiner’s Intention:
To test understanding of force balance.
Common Mistake:
Saying gravity is absent or ineffective.
Strategic Solving Advice
- Always separate force balance and motion analysis.
- Normal reaction depends on geometry, not always mg.
- System approach reduces complexity in many problems.
- Check whether speed or velocity is changing.
PART–4 (v) Completed.
PYQs covered so far: 25. Next set will complete the 30+ PYQ target.
📚 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.
© Mind Grow Magazine
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