Electric field- electrons are orbiting a stationary proton

Question

Four electrons are orbiting a stationary proton along a perfect circle with a constant speed  as shown below. Find the orbital speed and frequency of this circular motion if the radius of the orbit is . The elementary charge  and the electron mass .

Answer 1

Equate centripetal force with electric force (This problem is not physical as electrons do not orbit protons. Classical physics does not work here - Quantum Mechanics was necessary in order to explain electrons' behavior in atoms. Also 4 electrons don't occupy the same orbital - not important to problem, anyway)

For 1 electron:

m_ev²/r = k_eq_pq_e/r² = k_eq²/r²

rearrange to solve for v. I get

v = sqrt(k_eq²/r m) All the units mesh as given to get v in m/s (use k_e = 8.99 x 10⁹ Nm²/C²