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## Homework Statement

2 small spheres each having a mass of 0.1g are suspended from the same point on silk threads 20cm long. When given equal charges, they repel, resting 24cm apart. Calculate charge of each.

## Homework Equations

F(w)=mg(a)

F=kQ(1)Q(2)/d^2

k=8.987x10^9 N*m^2 / c^2

## The Attempt at a Solution

I converted grams to kilograms.. 1 x 10^-4 kg

kilograms to Newtons/weight..9.8*10^-4N

blah blah..

F=kQ(1)Q(2)/d^2

(7.35*10^-4N)(.24^2)(8.987*10^9 N*m^2/c^2)=Q^2

Q=6.86*10^-8C

http://i80.photobucket.com/albums/j199/pugfug90/physucks.gif [Broken]

Here's some work and a diagram. I am 99% sure that the answer is 6.9*10^-8 coulombs. However! I don't understand.. If I used trig to find half of the total force (in the triangle diagram).. why do I use the full distance?

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