Electrostatics Part 3

Consider two identical metallic spheres of radius R each having charge Q and mass m. Their centers have an initial separation of 4R. Both the spheres are given an initial speed of u towards each other. The minimum value of u, so that they can just touch each other is:
(Take k=‌

1

4πE0

and assume kQ2>Gm2 where G is the Gravitational constant)