# A point P lies on the axis of a ring of mass M/2 and radius R, at a distance 2 R from its centre O. A small particle starts form P and reaches O under gravitational attraction only, its speed at O will be:

Q: A point P lies on the axis of a ring of mass M/2 and radius R, at a distance 2 R from its centre O. A small particle starts form P and reaches O under gravitational attraction only, its speed at O will be:

(a) zero

(b) $\sqrt{\frac{2 G M}{R}}$

(c) $\sqrt{\frac{2 G M}{R}(\sqrt{5}-1)}$

(d) $\sqrt{\frac{G M}{R}(1 – 1/\sqrt{5})}$

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Ans: (d)