Chapter 18, Problem 17P

A 0.50-g oil droplet with charge $\text{+5}\text{.0 }\times {\text{ 10}}^{\text{-9}}\text{C}$ is in a vertical $\stackrel{\to }{E}$ field. In what direction should the $\stackrel{\to }{E}$ field point and what magnitude should it have so that the droplet moves at constant speed? Ignore the forces that air exerts on the droplet.