Question

At a distance of one centimeter from an electron, the electric field strength has a value

e. at what distance is the electric field strength equal to e/2?

Answer 1

we are asked in the problem to determine the distance of an electron in which the electric field strength is equal to e/3. we use the gravitational formula of E = m1m2/d^2
hence, 

e = m1m2/1 = k/1 =k
e/2 = k/d^2
e/2=e/d^2
d^2 = 2
d = sqrt 2 = 1.41 cm