Two identical charged spheres suspended from a common point by two massless strings of lengths l, are initially at a distance d ( d ≪ l) apart…

Two identical charged spheres suspended from a common point by two massless strings of lengths $\displaystyle l$, are initially at a distance $\displaystyle \mathrm{d}(\mathrm{d} \ll l)$ apart because of their mutual repulsion. The charges begin to leak from both the spheres at a constant rate. As a result, the spheres approach each other with a velocity $\displaystyle v$. Then $\displaystyle v$ varies as a function of the distance $\displaystyle x$ between the spheres, as :