Question

The ratio of the radius of gyration of a thin uniform disc about an axis passing through its centre and normal to its plane to the radius of gyration of the disc about its diameter is

• A. 2:1
• B. $\sqrt2:1$
• C. 4:1
• D. $1:\sqrt2$

Answer 1

Answer: (B)

$\sqrt2:1$

Answer 2

$I_1 = \frac{MR_2}{2} = MK_{12}$
$I_2 = \frac{MR_2}{4} = MK_{22}$
$K_1 = \frac{R}{\sqrt2}, K_2 = \frac{R}{2}$
$\frac{K_1}{K_2} = (\frac{1}{√2})(\frac{2}{1}) = \frac{2}{1}$