Electric Field to find Mass

1. Jan 18, 2010

krony23

1. The problem statement, all variables and given/known data
In a laboratory, a particle of charge -6C is held stationary because it is placed in an electric field E=(0,0,-15)N/C which suspends it against gravity. What is the mass of the particle? Give answer in kg.

2. Relevant equations
I THINK
E= F/q
F= ma

3. The attempt at a solution
Ok, so I haven't actually had a chance to attempt this yet because A) I don't understand the notation of E in this equation, so I don't know if it is acceptable to just use -15 for E, and B) if I even have the right equations to use, I don't know what the acceleration is. Please help

2. Jan 18, 2010

rock.freak667

It suspends it against gravity, so what is the relationship between the electric force and the mass?

3. Jan 18, 2010

krony23

I don't really get what that means about it though.

4. Jan 19, 2010

rock.freak667

The only forces acting on the mass are its weight and the electric force. If it is being suspended, what is the resultant force on it?