Example: (a) The distance between the centres of the carbon and oxygen atoms in the carbon monoxide (CO)g as molecule is 1.130x 10-10 metres. Locate the centre of mass of the molecule relative to the carbon atom. (b) Find the centre of mass of a homogeneous semicircular plate of radius a. Solution. (a) The centre of mass of the CO molecule will obviously lie on the line joining the C and O atoms. Let it be at a distance x from the carbon atom. Then, since the atomic weights of carbon and oxygen are respectively 12 and 16, we have 12x = 16(1.130 x 10-10 x) = 16 x 1.130 x 10-10 16x.