A ring of radius R carries charge $+q$ uniformly distributed on it. If a charge $- 90$ is released on ring's axis at a distance $\sqrt 3 R$ from its centre , the kinetic energy of $-90$ when it reaches the centre of ring will be :

Question

$(A)\;\frac{1}{4 \pi \in _0} \frac{q\;90}{\sqrt 3 R} \\ (B)\;\frac{1}{4 \pi \in _0} \frac{q\;90}{3R} \\ (C)\; \frac{1}{4 \pi \in _0} \frac{q\;90}{ R} \\ (D)\;\frac{1}{4 \pi \in _0} \frac{q\;90}{2 R} $