What Potential Difference Will Cause the Thread to Assume a 30° Angle?

[kuwaiteng]

hello !
i have an assignment on Electric Potential Energy , can anyone help me on solving it ?
the problem says : A small sphere with mass 2.70 g hangs by a thread between two large parallel vertical plates 5.00 cm apart.
The plates are insulating and have uniform surface charge densities . The charge on the sphere is q = 8.80×10^−6 C .
What potential difference between the plates will cause the thread to assume an angle of 30.0 with the vertical ?
see the figure :P

 

[semc]

draw the FBD of the sphere and resolve the forces in the x and y direction

 

[kuwaiteng]

thanx ,, i think i got the answer by drawing the diagram :
E = Mgtan(30)
F=E\q
V= E.d
it is right ?