Question

If the moment of inertia of a disc about an axis tangential and parallel to its surface be $I$, then what will be the moment of inertia about the axis tangential but perpendicular to the surface?

• A. $\frac {6}{5}I$
• B. $\frac {3}{4}I$
• C. $\frac {3}{2}I$
• D. $\frac {5}{4}I$

Answer 1

Answer: (A)

MI of disc about tangent in a place
$= \frac {5}{4}MR^2=I \, MR^2= \frac {4}{5}I$
$MI$ of disc about tangent perpendicular to plane
$I'= \frac {3}{2}MR^2$
$I'=\frac {3}{2}\left(\frac {4}{5}I\right)= \frac {6}{5}I$