Question

A solid sphere of mass `M`, radius `R` and having moment of inertia about as axis passing through the centre of mass as `I`, is recast into a disc of thickness `t`, whose moment of inertia about an axis passing through its edge and perpendicular to its plance remains `I`. Then, radius of the disc will be.
A. `(2 R)/(sqrt(15))`
B. `R sqrt((2)/(15))`
C. `(4 R)/(sqrt(15))`
D. `( R)/(4)`

Answer 1

Correct Answer - A
`(2)/(5) MR^(2) = (1)/(2) Mr^(2) + Mr^(2)`
`(2)/(5) MR^(2) = (3)/(2) Mr^(2)`
`r = (2)/(sqrt(15)) R`.