The electric force and the gravitational force.

[TKstreaker13]

What is the strength of an electric field that will balance the weight of a 2.5g plastic sphere that has been charged to -2.9nC ?

I know that F= ma and that E= Kq/r^2 and also that F= Kq1q2/(r^2). I just don't know how to relate an electric field equation using only mass and a charge?

 

[Doc Al]

I know that F= ma

OK. What would 'a' be in this case?

and that E= Kq/r^2 and also that F= Kq1q2/(r^2).

Those are expressions for the field from a point charge and the force between two point charges. You won't need them here. Hint: If the field is E, and the change is q, what's the electric force on the charge?

I just don't know how to relate an electric field equation using only mass and a charge?

What forces act on the plastic sphere? What's the net force?

 

[TKstreaker13]

a= acceleration

and i will need the F=qE equation

if the sphere is being balanced then the net force will be zero?

 

[Doc Al]

a= acceleration

I meant, what would be the value of the acceleration in this case.

and i will need the F=qE equation

Right. That's the one you need.

if the sphere is being balanced then the net force will be zero?

Exactly. What two forces act on the sphere?