How Is the Net Force Between Two Dipoles Calculated?

[lizardlad]

Homework Statement

Two identical dipoles, each of charge q and separation a, are a distance x apart as shown in Fig. By considering forces between pairs of charges in the different dipoles, calculate the net force between the dipoles. (a) Show that, in the limit a<<x, the force has a magnitude of 6kp^2/x^4, where p=qa is the dipole moment. (b) Is the force attractive or repulsive?

Homework Equations

F= kqq/r^2
E= kp/r^3

__|a_|_________|_a|___
--[- +]----------[- +]--
___|______x_____|____

The Attempt at a Solution

Not sure where to start

 

[SammyS]

Use coulomb's law to calculate the force exerted of each of the two charges in one dipole by the other dipole.