Question

The moment of inertia of a sphere of mass M and radius R about an axis passing thourgh its centre is 2/5 MR2. The radius of gyration of the sphere about a paralled axis to the above and tangent to the sphere is:

• A.
• B. $\frac { 3 } { 5 } \mathrm { R }$
• C. $\left( \sqrt { \frac { 7 } { 5 } } \right) \mathrm { R }$
• D.

Answer 1

Answer: (C)

$\left( \sqrt { \frac { 7 } { 5 } } \right) \mathrm { R }$

Answer 2

Moment of inertia of sphere about its tangent

$= \frac { 7 } { 5 } M R ^ { 2 } = M K ^ { 2 } \Rightarrow K = \sqrt { \frac { 7 } { 5 } } R$