A point charge `Q` is situated at point `B` on the ground. A point charge `q` of mass `m` is vertically dropped along line `AB` from a multi storey building of height `h`. Find the position of the point charge `q` when it is in equilibrium

Explanation

Let the distance of q from Q be d. Electric repulsion is shown as F in the figure.
For vertical equilibrium
F=mg
Using Coulomb.s law , we get :
`1/(4piepsilon_0)(Qq)/d^2=mg`
`rArr d=sqrt(1/(4piepsilon_0)(Qq)/(mg))`