Two fixed charge `A` and `B` of `5 mu C` each are separated by a distance of `6m` .C is the mid point of the line joining `A` and `B` .A charge `Q` of `-5 mu C` is shot perpendicular to the line joining `A` and `B` through `C` with a kinetic energy of `0.06 J`. The charge 'Q' comes to rest at a point `D` .The distance `CD` is