Physics II: Determine Electric Field Intensity for Equilibrium

[abelinkin1988]

Homework Statement

Two 3.0 g spheres are suspended by 9.0 cm long light strings. A uniform electric field is applied in the x direction. If the spheres have charges of -4.X10-8 C(coulomb) and +4.X10-8 C, determine the electric field intensity that enables the spheres to be in equilibrium at θ = 11°.


picture: http://www.webassign.net/sercp/p15-57.gif

So the units to the answer should be Newtons/Coulomb

The Attempt at a Solution

I am unclear on how to get the answer because i feel overwhelmed by formulas I can use. I've tried and the answer is definitely not 304,843.5. You see what I mean?

I would appreciate some ideas.


-Abe

 

[Delphi51]

Consider the forces on each charge. Sketch their vectors on a diagram. Write equations saying that the sum of the forces on each charge in the horizontal and vertical directions are zero (because they are not accelerating, F = ma = 0).

 

[abelinkin1988]

Consider the forces on each charge. Sketch their vectors on a diagram. Write equations saying that the sum of the forces on each charge in the horizontal and vertical directions are zero (because they are not accelerating, F = ma = 0).

Could you tell me how do i organize the number to get the answer? as in what equations do I use as well.