Coulomb's Law & Charge: Deriving Q Formula

[dom192]

Homework Statement

two pith balls are suspended on a wooden dowel and have the same origin point. the two balls are push away from each other and are equally negatively charge. the string have the length L and the two strings form angle (theta).

knowing

Fg= Gm1m2/r^2

Fe= kq1q2/r^2

Homework Equations

using the electrostatic constant k dervie the formula below.

Q= 2Lsin(theta) x square root of [mgtan(theta)/k]

The Attempt at a Solution

i found out that Fe= mgtan(theta) and Fe -Ft is the horizontal component. then i don't know wat to do after.

 

[dr_k]

Homework Statement

two pith balls are suspended on a wooden dowel and have the same origin point. the two balls are push away from each other and are equally negatively charge. the string have the length L and the two strings form angle (theta).

knowing

Fg= Gm1m2/r^2

Fe= kq1q2/r^2

Homework Equations

using the electrostatic constant k dervie the formula below.

Q= 2Lsin(theta) x square root of [mgtan(theta)/k]

The Attempt at a Solution

i found out that Fe= mgtan(theta) and Fe -Ft is the horizontal component. then i don't know wat to do after.

Good Afternoon dom192,

This is a statics problem. You need to draw a precise picture of the problem, then isolate one of the pith balls, and apply Newton's 2nd postulate for static equilibrium,
F_net = 0. These two equations will then allow you to solve for the unknown Q.

To get you started, here's a picture:

http://img109.imageshack.us/img109/6382/estatics1.jpg