Walker, Halliday & Resnick — Electric Fields: Problem 29

29 A charged cloud system produces an electric field in the air near Earth’s surface. A particle of charge $-2.0 \times 10^{-9}\text{ C}$ is acted on by a downward electrostatic force of $6.0 \times 10^{-6}\text{ N}$ when placed in this field. (a) What is the magnitude of the electric field? What are the (b) magnitude and (c) direction of the electrostatic force $F_{el}$ on a proton placed in this field? (d) What is the magnitude of the gravitational force $F_g$ on the proton? (e) What is the ratio $F_{el}/F_g$ in this case? (f) If the proton is released, what is the magnitude of its acceleration?