Rotational Motion – Phase 2 (Page 10)

Previous IIT / JEE Objective Questions + Final Strategy

This page contains authentic previous-year style objective questions from IIT-JEE & JEE Advanced, with short, sharp explanations and examiner logic.

PYQ-1 (IIT-JEE)

A disc and a ring of same mass and radius roll down an incline. Which statement is correct?

Method:

Acceleration a = g sinθ / (1 + I/MR²)

Disc: I/MR² = 1/2
Ring: I/MR² = 1

Answer: Disc reaches first

Examiner View: Checks understanding of I/MR².

PYQ-2 (JEE Advanced)

A rotating disc has angular momentum L. If moment of inertia is doubled suddenly, rotational KE becomes:

Logic:

K = L² / (2I)

Answer: Half of original

PYQ-3 (IIT-JEE)

In pure rolling motion on a rough surface, work done by friction is:

Key Idea:

Point of contact has zero displacement.

Answer: Zero

PYQ-4 (JEE Advanced)

A particle moving in straight line can have angular momentum about a point. True or False?

Reason:

Angular momentum depends on reference point.

Answer: True

PYQ-5 (IIT-JEE)

A body rotating with constant angular momentum has:

A) Constant angular speed
B) Constant KE
C) Constant I
D) None of these

Concept:

L = Iω → product constant only

Answer: D) None

PYQ-6 (JEE Advanced)

A disc slides on a rough surface and then rolls. Which statement is correct initially?

Physics:

Friction reduces v but increases ω.

Answer: Translational KE decreases, rotational KE increases

FINAL STRATEGY – EXAM HALL RULES

✔ First decide: Energy or Angular Momentum
✔ Fix reference axis clearly
✔ Write I/MR² immediately
✔ Check friction role (work or torque?)
✔ Eliminate options before calculation

LAST-MINUTE CHECKLIST (ROTATIONAL)

✔ Sudden event → Angular momentum
✔ Rolling ≠ slipping
✔ Angular momentum depends on axis
✔ KE may increase due to internal work
✔ Never mix linear & angular blindly

WHAT YOU HAVE MASTERED

✔ Intermediate concepts
✔ Board exam answers
✔ IIT basic → extreme problems
✔ Objective elimination
✔ Topper-level thinking

PHASE-2 COMPLETED SUCCESSFULLY ✅
Next: Phase 3 – Exam Mastery & Rank Boosting

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🔄 Rotational Motion – Phase 3 (Exam Mastery Series)

Advanced exam-oriented thinking series focusing on traps, execution, pressure handling, and topper strategies.

Phase 3 – Page 1
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