Three spiders are resting on the vertices of a triangular web. The sides of the triangular web have a length of a = 0.85 m, as depicted in the figure. Two of the spiders (S1 and S3) have +7.7 µC charge, while the other (S2) has

Question

−7.7 µC
charge.
a)What are the magnitude and direction of the net force on the third spider
(S3)
c)What are the magnitude and direction of the net force on the third spider (S3) when it is resting at the origin?

cant seem to get this one, what are the steps to do this?

Answer 1

F = k Q1 Q2/r^2

If all three sides are the same length a, we have an equilateral triangle with 60 degree interior angles
Q1=Q3 = Q
Q2 = -Q
find force on Q3
F due to Q1 in direction from Q1 through Q2 (repulsive)
F= k Q^2/a^2
F from Q2 on Q3 (attractive)
F= k Q^2 /a^2 same magnitude

so if x axis is along direction from Q1 to Q3 then
Fx = F - F cos 60
and if y is perpendiculat to x
Fy = F sin 60

Now move Q3 to the origin and do part c

Answer 2

so magnitude is (8.99E9*-7.7)/(.85)^2 ?

im still confused on distance?