A Christmas ornament made from a thin hollow glass sphere ha…

A Christmas ornament made from a thin hollow glass sphere hangs from a small hook at its surface. It is observed to oscillate with a frequency of 2.50 Hz in a city where g = 9.80 m/s2. What is the radius of the ornament? The moment of inertia of a hollow sphere of mass M and radius R about a point on its edge is 5MR2/3.