(a) What is the electric field 4.00 m from the center of the terminal of a Van de Graaff with a 3.00 mC charge, noting that the field is equivalent to that of a point charge at the center of the terminal? N/C
(b) At this distance, what force does the field exert on a 2.00C charge on the Van de Graaff's belt?
N

a)   E = 1.69 10⁶6 N / C,  b)  F = 3.38 10⁶ N

Explanation:

a)  In this exercise using Gauss's law we can consider the charge of the generator sphere as if it were at its center, therefore the electric field is

          E = k

let's calculate

         E = 9 10⁹ 3.00 10⁻³ / 4²2

         E = 1.6875 10⁶ N / C

          E = 1.69 10⁶6 N / C

b) let's calculate the electric force

          F = q E

          F = 2.00 1.69 10⁶

          F = 3.38 10⁶ N

this is a good question! i'll do some research and come back when i have the answer!