The Attempt at a Solution
Our teacher said we don't need to memorize the Moment of inertia formulas because there is always a table we can look up for most objects. However we ran into problem in the HW.
Where does the 1/2 come from? Is that something we were just suppose to know? And why is I is the same for a whole circle or 1/2 a circle or even 1/4 of a circle?