Proton-beam therapy can be preferable to X rays for cancer treatment (although much more expensive) because protons deliver most of their energy to the tumor, with less damage to healthy tissue. A cyclotron used to accelerate protons for cancer treatment repeatedly passes the protons through a 15-kV potential difference.
(a) How many passes are needed to bring the protons’ kinetic energy to 1.2x10^-11 J?
(b) What’s that energy in eV?