The position of the centre of gravity of a (i) Rectangular lamina and (ii) cylinder is
i) at intersection of diagonals and ii) mid-point of the flat surface of the cylinder
i) at intersection of the sides and ii) mid-point of the flat surface of the cylinder
i) at intersection of diagonals and ii) mid-point of the axis of the cylinder
i) at intersection of the sides and ii) mid-point of the axis of the cylinder
The C.G. for each is indicated below