Consider a uniformly charged ring in the xy plane, centered at the origin. The ring has radius a and positive charge q distributed evenly along its circumference.
Imagine a small metal ball of mass m and negative charge −q0. The ball is released from rest at the point (0, 0, d) and constrained to move along the z axis, with no damping. If 0 < d ≪ a, what will be the ball's subsequent trajectory?