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A uniformly charged ring of radius $3a$ and total charge $q$ is placed in $xy-$ plane centered at origin. A point charge $q$ is moving towards the ring along the $z-$ axis and has speed $v$ at $z = 4a$. The minimum value of $v$ such that it crosses the origin is
  • A$\sqrt {\frac{2}{m}} {\left( {\frac{1}{5}\frac{{{q^2}}}{{4\pi { \in _0}a}}} \right)^{1/2}}$
  • B$\sqrt {\frac{2}{m}} {\left( {\frac{1}{15}\frac{{{q^2}}}{{4\pi { \in _0}a}}} \right)^{1/2}}$
  • C$\sqrt {\frac{2}{m}} {\left( {\frac{4}{15}\frac{{{q^2}}}{{4\pi { \in _0}a}}} \right)^{1/2}}$
  • D$\sqrt {\frac{2}{m}} {\left( {\frac{2}{15}\frac{{{q^2}}}{{4\pi { \in _0}a}}} \right)^{1/2}}$
JEE MAIN 2019, Diffcult
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