DrKrunklehorn
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Homework Statement
Two identical, small spheres of mass 2.0g are fastened to the ends of a 0.6m long light, flexible, insulating fishline. The fishline is suspended by a hook in the ceiling at it's exact center. The spheres are each given the same electric charge. They are in static equilibrium, creating an angle of 30° between the halves of the string. Calculate the magnitude of the charge on each sphere.
Here's a sketch of the picture given on the worksheet:
Red lines are what I drew over the diagram to make a right triangle.
This being a bonus type question, I was given three possible answers and had to find out which one was the real one:
q =
3.7 x 10^-7 C or
1.2 x 10^3 C or
1.2 x 10^-3 C.
Homework Equations
Coulombs Law: F = k \ \frac{q_1 q_2}{r^2}
The Attempt at a Solution
First I converted the mass into kilograms: m = 0.002kg
Then I split the angle into two right triangles to get the distance between the spheres.
r/2 = Sin15 x 0.3 m
r = approx. 0.16m
Then I figured since the spheres are at rest, then a = 0 and Fg = Fe...so I tried coulombs law to solve for q:
F_{g} = F_{e}
mg = k \ \frac{q_1 q_2}{r^2}
\frac{mgr^2}{k} = q_1 q_2
I ended up with 2.6 x 10^-11...obviously way off any of the true answers.
Thanks for taking the time to read over all this. =D
Cheers - Krunklehorn