Assume a classical hydrogen atom, in which the electron orbits the proton in a circular path due to the Coulomb's force. Taking the mass of electron

Assume a classical hydrogen atom, in which the electron orbits the proton in a circular path due to the Coulomb's force. Taking the mass of electron to be 9 × 10−31???????? and the radius of the orbit to be 5.2 × 10−11 ????, calculate the speed of the electron in its orbit.
The gravitational force close to the surface of the Earth is described by ???????? = ???????? , where ???? = 9.8 ????/????2. If we want an electron to float very close to the surface of the Earth, what should be the sign and magnitude of the charge we should place at the center of the Earth? Take the mass of electron 9 × 10−31???????? and the radius of the Earth to be 6370 km.
A point charge ???? = 2 × 10−3 ???? is placed at the center of a cube with length ???? = 25 ????????. What is the flux passing through one side?