Q: 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
(a) $v = \frac{1}{2 R}\sqrt{\frac{1}{G m}}$
(b) $v = \sqrt{\frac{G m}{6 R}}$
(c) $v = \frac{1}{2 }\sqrt{\frac{G m}{R}}$
(d) $ v = \sqrt{\frac{4 G m}{R}}$
Ans: (c)