Pendulum Problem and steiner' law

[ChazyChazLive]

Homework Statement

A uniform circular disk whose radius R is 14.3 cm is suspended as a physical pendulum from a point on its rim. (a) What is its period? (b) At what radial distance r < R is there a pivot point that gives the same period? (give answer in cm)

Homework Equations

T= 2pi radical ( I / mgh )

The Attempt at a Solution

Okay, I already found part A using T= 2pi radical ( I / mgh )
Any help would be greatly appreciated =]

Part A: 0.849 s <-- It's correct.
I'm just stuck on Part B.

 

[Thaakisfox]

Use steiner' law to express the I through a parallel axis..

 

[rl.bhat]

You can find the radial distance by equating period of the disk to that of a simple pendulum.