# Electric field and static equilibrium

1. Mar 23, 2008

### Hockeyq12

1. The problem statement, all variables and given/known data

An object of mass m= 5.0g and charge Q= 45mC is attached to a string and placed in a uniform electric field that is inclined at an angle of 30.0 with the horizontal (see the figure). The object is in static equilibrium when the string is horizontal

2. Relevant equations

Find the magnitude of the electric field in (N/C) and then find the tension in the string

3. The attempt at a solution
I am not sure how to do this I think you would you the Coulombs equation kQ/r^2 but I do not know how to find r. Also I can not remember how to find tension

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2. Mar 23, 2008

### Staff: Mentor

You won't need Coulomb's law--that tells you the force between two point charges, which is not what you have here. Instead, what's the most basic relationship between electric field, charge, and electric force?

Also: The fact that the mass is in equilibrium should tell you something about the net force on it. Hint: Consider vertical and horizontal force components.