A grandfather clock has a pendulum that consists of a thin brass disk of radius

Question

A grandfather clock has a pendulum that consists of a thin brass disk of radius r and mass m that is attached to a long thin rod of negligible mass. The pendulum swings freely about an axis perpendicular to the rod and through the end of the rod opposite the disk, as shown in the figure below. If the pendulum is to have a period T for small oscillations, what must be the rod length L. (Use any variable or symbol stated above along with the following as necessary: g for the acceleration of gravity.)
L =  

Explanation / Answer

This is a physical (not simple) pendulum, for which you have the correct formula for the period.
For I: This is the moment of inertia of the mass about the pivot point of the pendulum, and equals the sum of the Icg of the disk plus the I of the CM of the disk about the pivot:

I =

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