- #1

- 2

- 0

## Homework Statement

Two tiny spheres of mass = 7.20 mg carry charges of equal magnitude, 72.0 nC , but opposite sign. They are tied to the same ceiling hook by light strings of length 0.530 m . When a horizontal uniform electric field E that is directed to the left is turned on, the spheres hang at rest with the angle between the strings equal to 50.0 degrees.

What is the magnitude E of the field?

## Homework Equations

Fe

_{1}= Eq

Fe

_{2}= (Kq1q2)/r

^{2}

Fg = mg

## The Attempt at a Solution

I assumed that the state it is in is in equilibrium so I set up:

ƩF = Fg + Fe1 + Fe2 + T = 0

ƩT

_{x}= Tcosθ - Fe1 + Fe2 = 0

θ being 65 degrees since I split the triangle made by the 50 degrees into 2 right triangles.

ƩT

_{y}= Tsinθ - mg = 0

T = (Fe1 - Fe2)/cosθ

T

_{y}= (Fe1 - Fe2)tanθ - mg = 0

Fe1 = mg/tanθ + Fe2

E = (mg/tanθ + kq1q2/r

^{2})/q

(I found r to be .448 using the right triangles I formed)

I plugged in all the given values and I've got...1.17 x 10^6

Which is wrong. Can someone please explain what I messed up on?