Consider two identical metallic spheres of radius R each having charge Q and mass m. Their centers have an initial separation of 4 R. Both the…

Consider two identical metallic spheres of radius $\displaystyle R$ each having charge $\displaystyle Q$ and mass $\displaystyle m$. Their centers have an initial separation of $\displaystyle 4 R$. Both the spheres are given an initial speed of $\displaystyle u$ towards each other. The minimum value of $\displaystyle u$, so that they can just touch each other is : (Take $\displaystyle k=\frac{1}{4 \pi \epsilon_0}$ and assume $\displaystyle k Q^2>G m^2$ where $\displaystyle G$ is the Gravitational constant)