Problem concerning a mass with charge in a homogeneous electric field

[youmei0426]

Homework Statement

As stated in the photo

Relevant Equations

For a homogenous field: E=F/q

I know how the answer is C, since E=F/q and F=ma=mg. However, I am a bit confused as to why my other method doesn't work. I thought that since the droplets are falling at a constant velocity, there is not net force, so according to E=F/q the electric field must be zero then? This seems like a really weird way of thinking but I can't tell what exactly went wrong in my reasoning... Thanks for the help!

 

[Mastermind01]

I thought that since the droplets are falling at a constant velocity, there is not net force, so according to E=F/q the electric field must be zero then?

Your first line is correct, since the droplets are falling at constant velocity the net force is zero. So think about the second equation, $E = \frac F q$. In this equation, what is F?

 

[kuruman]

I thought that since the droplets are falling at a constant velocity, there is not net force,

That is correct.

... so according to E=F/q the electric field must be zero then?

That is not correct. There is a difference between F and F_net. The F in E = F/q is the electric force not the net force. F_net is the sum of all the forces acting on the droplet.