A cyclotron accelerates protons in a magnetic field of $1.0\ \text{T}$. The protons leave when their circle reaches a radius of $50\ \text{cm}$. Take the proton's mass as $1.67 \times 10^{-27}\ \text{kg}$ and its charge as $1.6 \times 10^{-19}\ \text{C}$. The frequency of the alternating voltage needed, and the kinetic energy of the protons as they leave, are closest to