Which of these source charges will produce a maximum possible speed?

[MyNewPony]

Homework Statement

Your lab assignment is to use positive charge Q to launch a proton, starting from rest, so that it acquires the maximum possible speed. You can launch the proton from the surface of a sphere of positive charge Q and radius R, or from the center of a ring of charge Q and radius R, or from the center of a disk of charge Q and radius R.

a) We will choose to launch the proton from the surface of a sphere of positive charge Q and radius R.

b) We will choose to launch the proton from the center of a ring of charge Q and radius R.

c) We will choose to launch the proton from the center of a disk of charge Q and radius R.2. The attempt at a solution

I have no idea how to go about solving this. I'm assuming a) is the correct answer because it has the greatest surface area?

 

[tiny-tim]

Hi MyNewPony!

Find the potential energy in each case (calculated with energy at infinity = 0)