JEE Physics Rotational Mechanics — Moment of Inertia, Angular Momentum, Rolling Motion and MCQ Practice

Rotational Mechanics is one of the most important chapters in JEE Physics. In JEE Main 2024, 2 questions came from this chapter; JEE Advanced 2023 had 3 rotational problems. Mastering moment of inertia, angular momentum conservation, and rolling motion is essential for JEE 2027.

Moment of Inertia (I)

I = Sigma(mr²) for discrete masses | I = integral(r² dm) for continuous bodies

Analogue of mass for rotation. Depends on axis of rotation.

Standard Results (Memorise for JEE):

Theorems of Moment of Inertia

Parallel Axes Theorem: I = I_cm + Md2 (d = distance from CM axis)

Perpendicular Axes Theorem: I_z = I_x + I_y (for planar bodies only)

Torque and Angular Acceleration

Torque: tau = r x F (cross product) | Magnitude: tau = rF sin(theta)

Newton Law for Rotation: tau = I*alpha

Angular Momentum

L = I*omega (rigid body) | L = r x p (particle)

Conservation: When net torque = 0, L is conserved.

Classic: Ice skater pulls arms (I decreases, omega increases, L constant)

Rolling Motion Without Slipping

Condition: v = R*omega

KE_total = (1/2)mv2 + (1/2)I*omega2 = (1/2)mv2(1 + k2/R2)

Acceleration on incline: a = g sin(theta) / (1 + k2/R2)

Order reaching bottom (fastest first): Solid sphere > Solid cylinder > Hollow sphere > Hollow cylinder

Rolling Bodies Comparison

Practice MCQs – Rotational Mechanics

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Last updated: April 2026 | JEE Gurukul – Focused JEE preparation with concept clarity