Ive been working on this problem for a few hours and cant get the last few parts.

In a linear accelerator, protons are accelerated from rest through a potential difference to a speed of approximately 3.1 X 10^6 meters per second. The resulting proton beam produces a current of 2 X 10^-6 ampere.

I found part B and D (with respect to the answer of part A), but i cant get part A, which is: Determine the potential difference through which the protons were accelerated.

I also cant get part C, which is: The proton beam enters a region of uniform magnetic field B that causes the beam to follow a cemicircular path. Determine the magnitude of the field that is required to cause an arc of radius .1 meter.

Any help is appreciated. Thanks!