Ok, how should I go about this one?

[matt85]

Pendulum

A small 12.00g plastic ball is suspended by a string in a uniform, horizontal electric field with a magnitude of 10^3 N/C. If the ball is in equilibrium when the string makes a 30 ° angle with the vertical, what is the net charge on the ball?

Q = _________ C

I know Coloumb's Law, and I assume I want to implement it here somehow, however I don't know where to begin on setting this one up.

 

[matt85]

Oh, and here is the visual.

 

[Doc Al]

The ball is in equilibrium. What does that tell you?

 

[matt85]

That there is no force acting on it?

 

[andrewchang]

No, that isn't exactly the definition of equilibrium.

Equilibrium is when there is no _net_ force acting on it.

 

[Doc Al]

That there is no force acting on it?

That there's no net force acting on it. Or, in other words: The net force is zero.

Start by identifying all the forces acting on the ball, then set up the equations for equilibrium. (Analyze the x and y components separately.)