An ideal electric dipole is situated at the origin, and points in the z direction, as in...

An ideal electric dipole is situated at the origin, and points in the z direction, as in Fig. 3.36. An electric charge is released from rest at a point in the xy plane. Show that it swings back and forth in a semi-circular arc, as though it were a pendulum supported at the origin.²⁸

Reference figure 3.36