A point electric dipole with dipole moment p1 is placed at the origin of co- ordinates r= 0 and interacts with a second dipole p2. The position vector of the second dipole is r. Determine the energy of interaction U and the force F between these two dipoles. Which orientation of the dipoles and r provides a maximum of the interaction force |F| at fixed value of r ? Answers should be written in the spherical system of coordinates, related to the first dipole.