📚 IIT–JEE Physics Complete Learning Hub

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🔹 Core Physics Libraries

• 🔁 Simple Harmonic Motion (SHM) – Complete Library (IIT–JEE Advanced)
• 🌊 Mechanical Waves – JEE Advanced Objective Library
• 🧠 IIT–JEE Physics Complete Master Library

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🔹 Central Learning Platforms

• 🌐 Shaktimatha Learning Resource Hub
• 💬 Join Our WhatsApp Physics Learning Channel

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📌 Structured • Exam-Oriented • IIT–JEE Advanced Focused Learning

Stage–1 | Page–4
Constraints, Geometry & String–Pulley Logic

The hidden backbone of IIT/JEE mechanics

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Why Constraints Decide the Answer

In IIT/JEE, many problems look difficult not because of equations, but because of constraints.

• Strings cannot stretch
• Pulleys guide motion
• Geometry links displacements

If constraints are ignored, equations become meaningless.

Reality: Most wrong answers come from wrong constraint understanding.

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Golden Rules of Ideal Strings

• String length is constant
• Same string → same tension (if pulley ideal)
• If one end moves, the other must adjust

Exam Tip: Never assume motion direction — derive it from constraints.

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Geometry → Relationship Between Motions

When multiple bodies are connected:

• Displacement relation comes first
• Velocity is derivative of displacement
• Acceleration is derivative of velocity

Order always is: Displacement → Velocity → Acceleration

Never jump directly to acceleration.

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Most Common String Constraint Patterns

System	Key Constraint
Single pulley	Equal magnitude of velocity
Movable pulley	Velocity ratio 2:1
Multiple pulleys	Segment counting method

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Segment Counting Method (IIT Favourite)

Steps:

1. Count how many string segments support a body
2. Displacement is shared equally
3. More segments → less acceleration

Shortcut: Acceleration ∝ 1 / number of supporting segments

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Sign Convention – Silent Killer

Choose ONE positive direction and stick to it.

• All displacements must follow sign
• Velocities must follow same sign
• Accelerations follow same sign

Mistake: Changing sign midway to “match answer”

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How IIT Expects You to Think

1. Draw neat constraint diagram
2. Write length equation
3. Differentiate carefully
4. Apply Newton / Energy after constraint

Constraint first, force later.

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What Comes in Page–5?

• Typical IIT trap problems
• Wrong-but-tempting options
• How toppers eliminate options fast

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Stage–1 | Page–4 Completed Successfully ✅