Physics?? please help me??

Question

The three charges are held in place in the figure below, where L = 1.35 m.

http://www.webassign.net/walker/20-24alt.gif

(a) Find the electric potential at point P.

__ kV

(b) Suppose that a fourth charge, with a charge of 6.05 µC and a mass of 4.71 g, is released from rest at point P. What is the speed of the fourth charge when it has moved infinitely far away from the other three charges?

__ m/s

Answer 1

find out the potential due to earch charge at given distance and add.

for 2.75 and - 1.72 uc the distance is 1.35/2 while

for 3.45 uc the distance is  1.35Xsin 60

substitute in the equation for potential and add them algebrically

the potnetial due to + charge is + and due to negative charge it is negative,