Answer
(a) Both gravity and the electric force are long-range forces, and the strength of the force between two point particles depends on the distance in the same way: it decreases with the square of the distance ($F \propto 1/r^2$). Additionally, the gravitational force is proportional to the product of the masses of the particles, while the electric force is proportional to the product of their charges.
(b) Gravity is always an attractive force because mass is always positive, whereas the electric force can either attract or repel depending on the signs of the charges. Unlike mass, which cannot be negative, electric charge can be either positive or negative.
Work Step by Step
from the reading in the chapter - pretty straight forward.
