Q: Three identical bodies, each of mass *m*, are located at the vertices of an equilateral triangle with side *r*. The speed with which they move if they all revolve under the influence of one anotherâ€™s gravitation in a circular orbit circumscribing the triangle while still preserving the equilateral triangle ?

(a) $ \displaystyle \sqrt{\frac{G m}{3 r}} $

(b) $ \displaystyle \sqrt{\frac{G m}{ r}} $

(c) $ \displaystyle \sqrt{\frac{2 G m}{ r}} $

(d) $ \displaystyle \sqrt{\frac{G m}{2 r}} $

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Ans: (b)