Point Charge Repulsion from Spherical Conductor?

[Subhra99]

Homework Statement

A point charge e is braught near a spherical conductor of radius "a" having a charge "q".show that the particle will be repelled by the sphere unless its distance from the nearest point of its surface is less than (a/2) *√(e/q) approximately?

Homework Equations

The Attempt at a Solution

 

[Subhra99]

please help me with this