Find the moment of inertia of a rectangular plate with sides a and b about an axis perpendicular to the plate and passing through a vertex.
Choose the rectangular plate [see Fig.9-20] in the xy plane with sides on the x and y axes. choose the z axis perpendicular to the plate at a vertex.
From Problem 9.6 we have for the moments of inertia about the x and y axes,
Then by the perpendicular axes theorem the moment of inertia about the z axis is