Lesson 6 – Centre of Mass & System of Particles

FINAL REVISION · PART–4
Examiner View, Traps & Answer-Writing Strategy

This final revision page is designed to protect marks. Even if a student is nervous, this page ensures safe performance.

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1️⃣ What the Examiner Actually Tests

✔ Ability to identify system
✔ Ability to separate internal & external forces
✔ Application of COM law, not calculation
✔ Conceptual clarity under pressure

Examiner does NOT test speed or long algebra here.

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2️⃣ Top 10 Traps (Read Slowly)

1. Zero momentum ≠ zero force
2. Explosion ≠ change in COM path
3. Internal force ≠ COM acceleration
4. Long question ≠ hard question
5. Equal masses ≠ COM at midpoint always
6. Rotation ≠ translation of COM
7. COM velocity ≠ same in all frames
8. Frame mention ≠ ignore it
9. Numbers ≠ importance
10. Panic ≠ thinking

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3️⃣ Board Exam Answer-Writing (Very Important)

For long/short answers:

✔ Start by defining system
✔ Write COM law in words or formula
✔ Mention internal forces cancel
✔ Conclude in one clear sentence

This alone can fetch full marks.

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4️⃣ IIT-JEE Answer Strategy (Objective & Integer)

✔ First eliminate impossible options
✔ Use direction & sign logic
✔ Avoid calculation unless forced
✔ Trust laws over intuition

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5️⃣ Last 60 Seconds Before Exam Ends

Recheck only these:

✔ Frame choice correct?
✔ Internal forces ignored?
✔ Direction of acceleration sensible?

Do NOT re-solve entire question.

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6️⃣ Final Confidence Message to Students

You do not need to remember everything.
You need to remember the law.

ΣF_external = M a_cm

If you apply this calmly, Centre of Mass becomes a scoring chapter.

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🏁 FINAL CLOSURE – REVISION PART–4

This completes the ENTIRE REVISION SERIES for Lesson 6.

✔ Concepts clear
✔ Traps removed
✔ Confidence built
✔ Exam-ready mindset achieved

Lesson 6 is now fully sealed.

📘 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