Question

Two particles of equal mass go round a circle of radius R under the action of their mutual gravitational attraction. Find the speed of each particle.

Answer 1

The particles will always remain diametrically opposite so that the force on each particle will be directed along the radius. Consider the motion of one of the particles. The force on the particle is F = Gm²/4R² If the speed is v, its acceleration is v²/R.

Thus by Newton’s Law,