Finding theta for Coloumb's law suspension

[Zoidberg3001]

Homework Statement

Two spheres are suspended on strings and repel each other. Using the graphing function of your calculator setup and solve a formula to find theta.

The length of the rope is 3.0m, q = 1.0e4 and m = .2 kg.

Homework Equations

F=k*q1*q2/r^2

The Attempt at a Solution

Using Newton's second law I've tried several times to set up the formula to solve for theta but I am unable.

I know that the y component of tensions is equal to the force of gravity. Also that the X component of tension is equal to force caused by the repulsion of the two charges.

 

[BvU]

Equations look OK to me. Perhaps the instruction means they want you to solve numerically, not analytically ?

 

[Zoidberg3001]

We were told to find the equation, set it equal to zero and plug in our given mass, charge and length then find the x intercept with a graphing calucator. I get 60 degrees which is about twice what it should be.

 

[BvU]

Can't find any givens under

Homework Statement

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Perhaps you can use this thread to check if your calculator works properly

(Although I admit that for the numbers at the bottom of your sheet $\pi/3$ fits a lot better than $\pi/6$ :) )

 

[Zoidberg3001]

Oops, that's what I get for being in a rush. The length of the rope is 3.0m, q = 1.0e4 and m = .2 kg.

 

[BvU]

Hefty charge !

 

[Zoidberg3001]

Oh jeeze I just cannot type tonight. q = 1.0e-4

 

[BvU]

Well, as I said,

for the numbers at the bottom of your sheet $\pi/3$ fits a lot better than $\pi/6$ :)

So I'm at a loss. How do you know that it's not right ?

(can always try the check with this other thread to see if that fits...)

 

[Zoidberg3001]

My professor said that the angle should be about 30 degrees. It's possible I misheard though. I can't find an error so I think that might be the case.