Two particles of equal mass go round a circle of radius R under the action of their mutual gravitational attraction. The speed of each particle is
v=12R1Gm
v=Gm2R
v=12GmR
v=4GmR
Centripetal force provided by the gravitational force of attraction between two particles
i.e. mv2R=Gm×m(2R)2⇒v=12GmR