Electric Fields and Electric Charges?

Question

Imagine for a minute that the moon is held in its orbit about the Earth by electrical forces rather than by gravitation. What electrical charges -Q on the Earth and +Q on the moon are necessary to hold the moon in a circular orbit with a period of 27.3 days? The Earth-moon distance is 384,000 km and the mass of the moon is 7.35 ´ 1022 kg.

Answer 1

The force of attraction will be K*Q^2 / d^2

The centrifugal force is m*v^2 / d

Equate these to get

K*Q^2 / d^2 = m*v^2 / d

Q = √[m*v^2*d/K]

d is distance from center of the earth, 3.84*10^8  m

m = 7.35*10^22,  m K = 9*10^9 N*m^2/C^2

v must be in m/s  One orbit is 2*π*390.4*10^6m and takes 27.3 days or 2.359*10^6 sec.  The velocity is then 1040 m/s

Q = √[7.35*10^22*1.082*10^6*384*10^6/(9*10^9...

Q = 5.83*10^13 C  (if I did my arithmetic right)