PART–4 (ix) : IIT / JEE Previous Year Questions – Rank-Decider Set (With Tricks & Tips)

This section combines previous IIT/JEE questions with smart tricks, shortcut thinking, and examiner tips. Use these techniques to save time and avoid traps in the real exam.

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PYQ–41 (IIT–JEE Advanced)

Question:

A force F acts on a block of mass m for a very short time Δt. Which physical quantity determines the change in motion?

Core Idea:

Short-time force problems are NOT solved using F = ma.

Solution:

Change in motion depends on impulse.

Impulse = F × Δt = change in momentum

Hence, change in momentum determines the motion.

EXAM TRICK:

If force acts for a very small time → immediately switch to impulse–momentum.

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PYQ–42 (IIT–JEE Advanced)

Question:

A particle moves such that acceleration is always opposite to velocity. Describe the nature of motion.

Thinking Step:

Velocity decides direction of motion. Acceleration opposite to velocity reduces speed.

Solution:

The motion is retarded (decelerated).

QUICK TIP:

Opposite directions (v and a) ⇒ speed decreases.

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PYQ–43 (IIT–JEE Advanced)

Question:

A block pushed on a rough surface first accelerates and then moves with constant speed. Explain.

Hidden Concept:

Static friction vs kinetic friction.

Solution:

Initially: Applied force > friction ⇒ acceleration.

Later: Friction balances applied force ⇒ net force = 0 ⇒ constant speed.

EXAM TRICK:

Constant speed ALWAYS means net force is zero.

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PYQ–44 (IIT–JEE Advanced)

Question:

Compare accelerations of a vertically projected body at different points.

Trap:

Velocity changes, but force does not.

Solution:

Only gravity acts throughout the motion.

Acceleration magnitude remains constant (= g).

QUICK TIP:

Ignore velocity; focus on forces.

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PYQ–45 (IIT–JEE Advanced)

Question:

A block does not move even when a force is applied. Where does the applied force go?

Concept:

Self-adjusting nature of static friction.

Solution:

Static friction equals applied force (up to its maximum value).

Net force = 0 ⇒ block remains at rest.

EXAM TRICK:

Static friction is NOT always μmg.

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MASTER TRICKS FOR LAWS OF MOTION (SAVE THIS)

• Very short time force ⇒ use impulse, not F = ma
• Constant velocity ⇒ net force = 0
• Acceleration depends on force, not velocity
• Static friction adjusts itself automatically
• Velocity zero does NOT mean acceleration zero
• Opposite directions of v and a ⇒ speed decreases

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PART–4 (ix) Completed (With Tricks & Tips).
Total PYQs covered: 45+
This level is more than sufficient for IIT–JEE Advanced.

📚 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.

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🎯 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

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📘 Complete Series: How IIT Toppers Think (Part 1–25)

Click on any part below to start learning. It is recommended to read in order.

1. Part 1 – Introduction to Topper Thinking
2. Part 2 – Understanding the Problem Statement
3. Part 3 – Visualization & Physical Sense
4. Part 4 – Role of Acceleration & Forces
5. Part 5 – Free Body Diagram Thinking
6. Part 6 – Method Selection Strategy
7. Part 7 – Avoiding Formula Traps
8. Part 8 – System Approach Mindset
9. Part 9 – Friction & Constraint Thinking
10. Part 10 – Time vs Accuracy Balance
11. Part 11 – Common Thinking Mistakes
12. Part 12 – Decision Flow in Tough Problems
13. Part 13 – Eliminating Wrong Options
14. Part 14 – Handling Multi-Concept Questions
15. Part 15 – Pressure Handling in Exam Hall
16. Part 16 – Speed Building Without Guessing
17. Part 17 – Extreme Case Thinking
18. Part 18 – Logical Shortcuts vs Blind Tricks
19. Part 19 – Advanced Reasoning Techniques
20. Part 20 – Rank-Deciding Thought Patterns
21. Part 21 – Physics Intuition Development
22. Part 22 – Eliminating Panic in Tough Questions
23. Part 23 – Last-Minute Thinking Strategy
24. Part 24 – Mistake-Proof Problem Solving
25. Part 25 – Final Topper Framework

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🧠 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

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This library is a long-term asset for serious Physics learners.
© Mind Grow Magazine