# Homework Help: Finding theta for Coloumb's law suspension

1. Jan 27, 2015

### Zoidberg3001

1. The problem statement, all variables and given/known data
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.

2. Relevant equations
F=k*q1*q2/r^2

3. 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.

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Last edited: Jan 27, 2015
2. Jan 27, 2015

### BvU

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

3. Jan 27, 2015

### 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.

4. Jan 27, 2015

### BvU

Can't find any givens under
1. The problem statement, all variables and given/known data
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 $\pi/6$ :) )

5. Jan 27, 2015

### 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.

6. Jan 27, 2015

### BvU

Hefty charge !

7. Jan 27, 2015

### Zoidberg3001

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

8. Jan 27, 2015

### BvU

Well, as I said,
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...)

9. Jan 27, 2015

### 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.