JEE Main202127 Jul 2021Morning ShiftPhysicsRotational MotionActual
The figure shows two solid discs with radius R and r respectively. If mass per unit area is the same for both, what is the ratio of M I of bigger disc around axis A B (Which is ⊥ to the plane of the disc and passing through its centre) of M I of smaller disc around one of its diameters lying on its plane? Given M is the mass of the larger disc. ( M I stands for a moment of inertia)
Options
- AR 2 :   r 2
- B2 r 4 :   R 4
- C2 R 2 :   r 2
- D2 R 4 :   r 4
Correct answer
D. 2 R 4 :   r 4
Step-by-step solution
Ratio of the moment of inertia = 1 2 M R 2 1 4 m r 2 = 2 σπ R 2 R 2 σ π r 2 r 2 = 2 R 4 r 4