1. The problem statement, all variables and given/known data A mass distribution in the positive x region of the xy-plane and in the shape of a semicircle of radius a, centred on the origin, has mass per unit area k. Find, using plane polar coordinates, its moments of inertia about the x and y axes. 2. Relevant equations 3. The attempt at a solution I know that I=∫r^2.dm dm=k.dA=k.r.dr.dθ in polar coordinates. So I=k∫dθ∫r^3.dr But I'm not sure about the limits, or how to differentiate between the moments of inertia about the x and y axes. Any help would be brilliant.