Lesson 6 – Centre of Mass & System of Particles

Objective Questions – Set 4
(Assertion–Reason & Advanced MCQs)

This set develops IIT-level logical clarity. Do not rush — read both Assertion and Reason carefully.

Assertion–Reason Key:
A) Both A and R are true, and R explains A
B) Both A and R are true, but R does not explain A
C) A is true, R is false
D) A is false, R is true

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Q1. (Assertion–Reason)

Assertion (A): If the net external force on a system is zero, the centre of mass moves with constant velocity.

Reason (R): Acceleration of centre of mass depends only on external forces.

Correct Option: A

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Q2. (Assertion–Reason)

Assertion (A): The centre of mass of a body can lie outside the material of the body.

Reason (R): Centre of mass depends on mass distribution, not on shape alone.

Correct Option: A

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Q3. (Assertion–Reason)

Assertion (A): During an explosion of a projectile in air, the centre of mass follows the same path as before explosion.

Reason (R): Explosion involves only internal forces.

Correct Option: A

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Q4. (Assertion–Reason)

Assertion (A): Zero momentum of a system implies zero acceleration of centre of mass.

Reason (R): Acceleration of centre of mass depends on the value of momentum.

Correct Option: C

Trap: Momentum value ≠ force acting.

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Q5. (Multiple Correct)

Which of the following statements about centre of mass are correct?

A) Internal forces can change COM motion
B) External forces determine COM acceleration
C) COM velocity may differ in different inertial frames
D) COM acceleration is same in all inertial frames

Correct Answers: B, C, D

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Q6. (Multiple Correct)

A system of particles is isolated. Which quantities are conserved?

A) Linear momentum
B) Kinetic energy
C) Velocity of centre of mass
D) Acceleration of centre of mass

Correct Answers: A, C, D

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Q7. (Advanced Concept MCQ)

Two equal and opposite forces act on a rigid body. Which are possible outcomes?

A) Translation of COM
B) Rotation of body
C) Change in momentum
D) Zero acceleration of COM

Correct Answers: B, D

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Q8. (Advanced MCQ)

In a non-inertial frame, which modification is required to apply COM laws?

A) Ignore internal forces
B) Add pseudo forces as external forces
C) Use momentum conservation only
D) Change reference frame to inertial

Correct Answer: B

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ASSERTION–REASON MASTER TIPS

✔ First judge Assertion alone
✔ Then judge Reason independently
✔ Finally check cause–effect link
✔ Avoid word-based assumptions
✔ COM questions always depend on external forces

📘 Centre of Mass & System of Particles – Complete Physics Library

This library is a complete learning package for Intermediate + IIT JEE Physics covering Centre of Mass and System of Particles.

It includes theory, solved examples, objective questions, IIT-level problems, revision strategies, tricks, and exam-oriented guidance.

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📂 Stage 1: Intermediate Complete Notes (Concept Foundation)

1. Part 1
2. Part 2
3. Part 3
4. Part 4
5. Part 5
6. Part 6
7. Part 7
8. Part 8
9. Part 9
10. Part 10

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📂 Stage 2: Advanced Concepts & Applications

11. Part 11
12. Part 12
13. Part 13
14. Part 14
15. Part 15
16. Part 16
17. Part 17
18. Part 18
19. Part 19
20. Part 20

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📂 Stage 3: Objective Questions, Tough Problems & Revision

21. Part 21
22. Part 22
23. Part 23
24. Part 24
25. Part 25
26. Part 26
27. Part 27
28. Part 28
29. Part 29
30. Part 30
31. Part 31
32. Part 32
33. Part 33
34. Part 34
35. Part 35
36. Part 36
37. Part 37
38. Part 38
39. Part 39
40. Part 40
41. Part 41
42. Part 42
43. Part 43
44. Part 44
45. Part 45
46. Part 46
47. Part 47
48. Part 48
49. Part 49
50. Part 50
51. Part 51
52. Part 52
53. Part 53
54. Part 54
55. Part 55
56. Part 56
57. Part 57

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Prepared by: Shaktimatha Learning 🌱
Vision: Concept clarity • Logical thinking • Exam excellence