PART–4 (iv) : IIT / JEE Previous Year Questions – Set 4
This set focuses on conceptual twists, free body diagrams, and hidden examiner traps. Colors are kept soft and academic to improve long-reading comfort.
PYQ–16 (IIT–JEE)
Question:
A block of mass m is resting on a smooth horizontal surface. Another block of mass m is placed on it. The lower block is pulled with a constant force F. Find the acceleration of the upper block if there is no slipping.
Method Selection:
Since there is no slipping, both blocks move together. Treat them as a single system.
Solution:
Total mass = 2m
Net force = F
Using F = ma:
a = F / 2m
Examiner’s Intention:
To check whether the student identifies conditions of no relative motion.
Common Mistake:
Applying friction equations without checking slipping condition.
PYQ–17 (IIT–JEE)
Question:
A block is projected up a rough inclined plane with initial velocity u. Find the acceleration during its upward motion.
Method Selection:
Resolve forces along the incline. Both gravity and friction act downward.
Solution:
Forces down the plane:
mg sinθ + μmg cosθ
Using F = ma:
a = g (sinθ + μ cosθ) (down the plane)
Examiner’s Intention:
To test correct direction of friction during upward motion.
Common Mistake:
Taking friction upward instead of downward.
PYQ–18 (IIT–JEE)
Question:
A body of mass m is kept inside a lift which is in free fall. What is the apparent weight of the body?
Method Selection:
Use apparent weight concept in non-inertial frames.
Solution:
In free fall, acceleration a = g downward.
Apparent weight:
N = m(g − g) = 0
Examiner’s Intention:
To test extreme case of apparent weight.
Common Mistake:
Writing N = mg even during free fall.
PYQ–19 (IIT–JEE)
Question:
A horizontal force acts on a body. The velocity increases but acceleration decreases with time. Which statement is correct?
Method Selection:
Conceptual reasoning based on Newton’s Second Law.
Solution:
Since acceleration decreases, net force must be decreasing.
Thus, opposing forces like friction must be increasing.
Examiner’s Intention:
To test relation between force and acceleration, not velocity.
Common Mistake:
Linking force with velocity instead of acceleration.
PYQ–20 (IIT–JEE)
Question:
A body is acted upon by two equal and opposite forces. Can the body still accelerate? Explain.
Method Selection:
Conceptual reasoning using net force.
Solution:
If forces are equal and opposite and act on the same body, net force is zero.
Therefore, acceleration is zero.
Examiner’s Intention:
To check understanding of force balance.
Common Mistake:
Confusing action–reaction pair with balanced forces.
Directional Thinking Tips
- Acceleration depends on net force, not motion.
- Friction direction depends on relative motion.
- Free fall is a special case of Newton’s Second Law.
- Always check extreme or limiting cases.
PART–4 (iv) Completed.
PYQs covered so far: 20. Next sets will complete 30+ years coverage.
📚 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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