Hint: The electrostatic force of attraction between positively charged nucleus and negatively charged electrons (Coulombian force) provides necessary centripetal force of revolution.
Step 1: Find the value of the Bohr radius.
By Bohr's postulates in the ground state, we have;
Step 2: Find the potential energy and kinetic energy.
The potential energy is given by;
Now, for a spherical nucleus of radius R.
Step 3: Find the value of the Bohr radius for R.
If R<rB, same result.
If R>>rB, the electron moves inside the sphere with radius r'B (r'B=new Bohr radius).