Bài tập về quả lắc đồng hồ

Mình có bài vật lý bằng tiếng Anh sau mong mọi người giải đáp giúp:

A pendulum is constructed as a light thin-walled sphere filled up with water and suspended from the ceiling by a rigid rod of negligible mass. The radius of the spherical container is R and the distance between the pivot point and the center of mass of the system is L. The period of small oscillations is [tex]T_0[/tex].
Due to a temperature drop in the room the water froze and the pendulum began to oscillate with a different frequency, corresponding to the period [tex]T_{1}[/tex]. Determine [tex]\frac{T_{1}}{T_{0}}[/tex] if  [tex]\frac{L}{R}=2[/tex]. Neglect the viscosity (friction) of the water and the change of its volume after freezing.

Cảm ơn mọi người nhiều.