What magnetic field would be necessary to require 230-MeV protons to revolve in a circle...

What magnetic field would be necessary to require 230-MeV protons to revolve in a circle of 15 m? (See Problem 56.)

Reference of problem 56.

Using the result of the previous problem, show that the radius of a particle's circular path having charge q traveling with speed v in a magnetic field perpendicular to the particle's path is . What happens to the radius as the speed increases as in a cyclotron?