It can be both flat or it can be when you have new eyeglasses on and you look down it makes you think the ground looks like that but its not
Im not 100% sure but i think its bromine.
Hope this helps ^_^
We divide the thin rectangular sheet in small parts of height b and length dr. All these sheets are parallel to b. The infinitesimal moment of inertia of one of these small parts is

where

Now we find the moment of inertia by integrating from

to

The moment of inertia is

(from (-a/2) to

(a/2))