- #1

- 14

- 1

## Homework Statement

Two m = 4.0 g point charges on 1.0-m-long threads repel each other after being charged to q = 80 nC , as shown in the figure. What is the angle θ? You can assume that θ is a small angle.

## Homework Equations

F

_{e}=kq

^{2}/r

^{2}

F=ma

F

_{g}=mg

## The Attempt at a Solution

Equation 1:[/B]

r = 2sinθ

F

_{e}=kq

^{2}/(2sinθ)

^{2}

**Equation 2:**

tanθ=F

_{e}/F

_{g}

F

_{g}tanθ=F

_{e}

**Combining Them:**

F

_{g}tanθ=kq

^{2}/(2sinθ)

^{2}

F

_{g}tanθ=kq

^{2}/(4(sinθ)

^{2})

(sinθ)

^{2}tanθ=kq

^{2}/(4F

_{g})

(sinθ)

^{2}tanθ=kq

^{2}/(4mg)

Okay, so now I have an equation with all the thetas on one side. So I tried to plug it into Wolfram Alpha to solve for theta, but it is giving me some really weird results. I'm not quite sure where I went wrong. Any help is greatly appreciated! Here's the Wolfram Alpha link. Thanks!

http://www.wolframalpha.com/input/?...*(8*10^-9)^2/(4*4*10^-3*9.8)+for+x+in+degrees