2. Potential from charge distribution A washerthat is, a disk with a hole in ithas inner radius a and outer radius b. The washer has a total charge Q > 0 spread uniformly on its surface. It is located in the my plane centered on the origin. (a) Find the potential at any point on the z axis, assuming V = 0 at innity. Show that your expression is approximated by the potential due to a point charge when |z| >> I). (b) Suppose a proton (charge +8, mass m) is placed on the z axis at (O, U, a) and then released. How fast will the proton be moving when it is very far from the washer? (Assume it's not so fast as to require relativistic equations.)