Centre of Mass of Two Particle System #8211; Consider the two particles system in which two masses m<sub>1</sub> and m<sub>2</sub> are separated by a distance d. The Centre of mass (CM) divides internally the line joining two particle (or masses) in inverse ratio of their masses. PR = m<sub>2</sub>d/m<sub>1</sub> + m<sub>2</sub> and QR = m<sub>1</sub>d/m<sub>1</sub> + m<sub>2</sub>