Solution Due to the mirror symmetry about the x axis, the cm must lie along the x axis If the hole is filled with a disk of the same material of radius r, the cm of composite disk is at the origin of the coordinate system mx+mlx x=0 CM for the big +m circular plate DxD R (-R)==R 丌(2R)2-mR2Solution: Due to the mirror symmetry about the x axis, the cm must lie along the x axis. If the hole is filled with a disk of the same material of radius R, the cm of composite disk is at the origin of the coordinate system. R R R R R x m m x D x D x 3 1 ( ) (2 ) ( ) 2 2 2  − = − − = − =    D x D D x x c m m m x m x x + + = 0 = CM for the big circular plate ?