
The time period of oscillation of physical pendulum is given by
T=2πMglI...(1)
Where, I is the moment of inertia of ring about given axis and l is the distance of centre of mass of ring from the axis of rotation.
Moment of inertia of ring in its plane is given by
I1=Ic+Md2=MR2+MR2=2MR2
Moment of inertia of ring perpendicular to its plane is given by
I2=Ic+Md2=2MR2+MR2=23MR2
Now the ratio of time period is given by
T2T1=I2I1
⇒T2T1=23MR22MR2
⇒T2T1=34=32