Lesson 7 – Momentum & Collisions

Phase 3: Exam Mastery (Advanced)
Page 12 – Objective 6 (Mixed Concepts & IIT Thinking)

This page contains integrated objective questions combining Momentum, Energy, Centre of Mass and exam logic. These questions are designed to develop IIT-level thinking, not just formula application.

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Q1. (IIT-JEE Advanced – Mixed Concept)

A particle explodes into two fragments while moving on a smooth surface. Which of the following quantities remain unchanged immediately after explosion?

• A) Velocity of each fragment
• B) Momentum of each fragment
• C) Velocity of centre of mass
• D) Total momentum of system

✔ Correct Options: C, D

Key Thinking: Internal forces cannot affect COM motion.

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Q2. (Graph-Based Objective)

If momentum versus time graph of a particle is a horizontal straight line, which conclusion is correct?

• A) Net force is zero
• B) Velocity is zero
• C) Acceleration is zero
• D) Kinetic energy is zero

✔ Correct Options: A, C

Trap: Constant momentum ≠ zero velocity.

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Q3. (Lengthy but Conceptual – IIT)

Two blocks connected by a spring are initially at rest. The spring is compressed and then released. Which of the following statements is correct?

• A) Total momentum remains zero
• B) Both blocks move with same speed
• C) Kinetic energy is conserved
• D) Centre of mass remains at rest

✔ Correct Options: A, D

Insight: Internal spring force cannot move COM.

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Q4. (Velocity Comparison – Trap)

Two particles of unequal masses collide elastically. Which of the following must be true?

• A) Heavier particle always has smaller speed
• B) Lighter particle always reverses direction
• C) Relative speed of separation equals approach
• D) Total kinetic energy remains constant

✔ Correct Options: C, D

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Q5. (No Calculation – Pure Logic)

Which statement best explains why momentum is more useful than energy in collision problems?

• A) Momentum is always zero
• B) Momentum depends on direction
• C) Momentum conservation applies in more situations
• D) Momentum is scalar

✔ Correct Answer: C

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🧠 How IIT Toppers Think (Objective 6)

✔ Ask: external force present or not?
✔ Think COM first, particles later
✔ Graph questions → slope = force
✔ Internal energy release ≠ momentum change
✔ Eliminate impossible options calmly

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🎯 Objective Mastery Completed

With Objective–6, you have covered:
✔ Simple → hardest objectives
✔ Single, multi-correct, AR, graph, logic
✔ True IIT Advanced thinking

👉 Next: Final Revision (4 Parts) + “How to Score Full Marks from This Chapter”