Question

The radius of gyration of a body about an axis at a distance 6 cm from its centre of mass is 10 cm. Then, its radius of gyration about a parallel axis through its centre of mass will be :

• A. 80 cm
• B. 8 cm
• C. 0.8 cm
• D. 80 m

Answer 1

Answer: (B)

8 cm

Let radius of gyration for the axis not passing through center of mass be $r$ and that for the axis passing through the center of mass be $k$ and the distance between the two parallel axes be $a$.

Parallel axes theorem gives:

$m{r}^2=m(k^2+a^2)\Rightarrow r^2=k^2+a^2$.

$\Rightarrow k=\sqrt{{10}^2-6^2}=8cm$.

Thus, option B is the correct answer.