Practice portal › Rotational Motion › Moment of Inertia

The mass per unit area of a circular disc of radius a is σ(r)=A+Br. Its moment of inertia about an axis perpendicular to the plane and through its centre is

Asked in JEE Main 8th April 1st Shift 2019 · Composite and cavity bodies

• (1) 2π a⁴((aA)/4+B/5)
• (2) 2π a⁴(A/4+B/5)
• (3) 2π a⁴(A/4+(aB)/5)
• (4) π a⁴(A/4+(aB)/5)

Step-by-step solution

Why the other options are wrong

• (1) Comes from attaching the extra length a to the A term rather than the B term.
• (2) Comes from dropping the length factor a that the B term needs for correct dimensions.
• (4) Comes from using π a⁴ instead of 2π a⁴ from the 2π r area element.

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.