The drawing shows four point charges. The value of q is 2.2 µC, and the distance d is 0.94 m. Find the total p

Question

The drawing shows four point charges. The value of q is 2.2 µC, and the distance d is 0.94 m. Find the total potential at the location P. Assume that the potential of a point charge is zero at infinity.

IMAGE:
http://www.webassign.net/cj/p19-16.gif...

Now I found that

"The key to this problem is the principle of superposition, which states that the interaction of two charges is unaffected by the presence of other charges. This applies to forces, fields, and potentials. So to calculate the total ppotential at P, first calculate the potential at point P due to each of the four charges, ignoring the other charges. Then add them all up. "
for this answer, but it did not help me much, still did not understand, nor got the answer right.

http://answers.yahoo.com/question/index;...

Help? Thanks!

Answer 1

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in general
V=Fd/Q= k sum[(qi/(Ri)^2)Ri] (i=1 to 4)
V= k sum[(qi/(Ri))] (i=1 to 4) since q1=q2=q3=q4
V=4k qi/(1/R1 +1/R2 +1/R3 +1/R4 )

k=8.854×109 N m^2 /C^2