A small sphere of mass m = 7.00 g and charge q1 = 31.7 nC is attached to the end

Question

A small sphere of mass m = 7.00 g and charge q1 = 31.7 nC is attached to the end of a string and hangs vertically as in the figure. A second charge of equal mass and charge q2 = 58.0 nC is located below the first charge a distance d = 2.00 cm below the first charge as in the figure.

(a) Find the tension in the string.
N

(b) If the string can withstand a maximum tension of 0.180 N, what is the smallest value d can have before the string breaks?
cm

AHHHHH!!!!!!!!!!!!!!!!!!!! (mathametically challanged_)

Explanation / Answer

Force between the two charges is F= 9x109x31.7x58x10-18x10^4/4 = 0.041 N

gravitational force= mg= 7/1000 x 10 = 0.07 N

so tension in the string = 0.041+0.07=0.111 N

if T=0.18

F=0.18-0.07=0.11 N

so d^2= 9x109x31.7x58x10-18x10^4/0.11

smallest value of d=1.226 cm

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