mechanics and electrostat

After some time the ball have some velocity.At this pt we can say that it experiences 3 normal forces.
Let the ball subtend an angle θ at this pt,with the st. line passing through original position and centre.
1)due to wt(mg)-remains const.
2)qEcosθ-to balance force in radial direction due to electric field.
3)it also experiences a normal force to counter act the centrifugal force caused due to rotation.

To calc. value of (3)(ie value of velocity):
Work done by elec. field=increase in KE[use integration of sinθ component of electric field]

Then (2) and (3) act along same directions, therefore net force along radial direction=qEcosθ-mv²/R
then to find θ find min. value of this net force,as the wt. component remains const.

After simple calculations ans=Rθ=Rcos^-12/3=Rtan^-1√5/2