Past exam of the physics course of the year 1 of the natural sciences course of the University of Cambridge / 2014 / Paper 1 / A2

For this equal-mass Coulomb circular orbit, let $s$ be the separation and $k_e=1/(4\pi {ϵ}_0)$. Each particle describes a circle of radius $s/2$ about the centre of mass. Coulomb's law and centripetal acceleration giveUsing $s$ as each particle's orbital radius would miss the equal-mass two-body motion.