Solving for Electric Field Strength & Direction of Charged Sphere

[Lydia22]

Homework Statement

What are the strength and direction of an electric field that will balance the weight of a 1.0g plastic sphere that has been charged t0 -3nC ?

Homework Equations

E= F/q

The Attempt at a Solution

Newton's laws on the charged sphere

ƩFnet(y) = F -mg=0
F=mg\
F=qE
E = mg/q
=[(0.003kg)(9.8m/s^2)]/(3.0x10^-9C)
=3x10^6 N/c
how do i conclude on the direction?

 

[I like Serena]

Hi Lydia22!

You have already used what the direction must be.
So you only have to make your conclusion explicit.

In your first line you have ƩFnet(y) = F -mg=0, which is the condition for the sphere to be in balance.
This implies that the electric force is equal and opposite to the force of gravity.
Since q is positive, that also holds true for the electric field.