Question

A circular ring of radius R with uniform positive charge density λ per unit length is fixed in the Y-Z plane with its center at the origin O. A particle of mass m and positive charge q is projected from the point P (√3R,0,0) on the positive X-axis directly towards O, with initial velocity v. Find the smallest value of the speed v such that the particle does not return to P.

Answer 1

Initial electric potential energy = q.V_p

for minimum velocity, final kinetic energy = 0 

By conservation of Energy,