IB Physics-Theme D2-Paper-2-A proton is moving in a region of uniform magnetic field

A proton is moving in a region of uniform magnetic field. The magnetic field is directed into the plane of the paper. The arrow shows the velocity of the proton at one instant and the dotted circle gives the path followed by the proton.
a. Explain why the path of the proton is a circle.
b. The speed of the proton is 2.0 × 10 m s and the magnetic field strength B is 0.35 T. Show that the radius of the path is about 6 cm.
c. 1c. Calculate the time for one complete revolution.
d. d. Explain why the kinetic energy of the proton is constant.
Topic 6 -Circular motion-Playlist