Find the center of the mass of a rectangular material of horizontal length a and vertical width b made up of a material of nonuniform find the center of density. the density is such that when the rectangle is placed in the xy-plane, the density is given by p(x, y)poxy. (assume that the +x-axis is to the right and the ty-axis is up along the page. further assume the origin is at the lower left corner of the rectangle. use the following as necessary: a and b.) xcm-