A uniformly charged ring of radius 3a and total charge q is placed in xy-plane centred 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:

Options

A. `sqrt2/m (4/15 q^2/(4piepsilon_0a))^(1//2)`
B. `sqrt2/m (1/5 q^2/(4piepsilon_0a))^(1//2)`
C. `sqrt2/m (2/15 q^2/(4piepsilon_0a))^(1//2)`
D. `sqrt2/m (1/15 q^2/(4piepsilon_0a))^(1//2)`

Answer

A