Q 11-06-073JEE MainJEE Main 2025 (28 Jan, Shift 1)Easy
Two iron solid discs of negligible thickness have radii $R_1$ and $R_2$ and moments of inertia $I_1$ and $I_2$, respectively. For $R_2 = 2R_1$, the ratio of $I_1$ and $I_2$ would be $1/x$, where $x$ = ______.
Numerical value type. Enter your answer.
Answer: 16
Same material and the same (negligible) thickness, so mass $\propto$ area $\propto R^2$.
$$I = \frac{1}{2}MR^2 \propto R^2\cdot R^2 = R^4$$
$$\frac{I_1}{I_2} = \left(\frac{R_1}{R_2}\right)^4 = \frac{1}{16}$$
$x = 16$
Solution by Sreeraj P, M.Sc Physics