1. The problem statement, all variables and given/known data 1. A positive charge of magnitude 2 microC is at the origin. (b)How much work must be done by an outside agent to bring a 3 microC charge from infinity to r=4, assuming that the 2 microC charge is held fixed at the origin ? (c) How much work must be done by an outside agent to bring the 2 microC charge from infinity origin if the 3 microC charge is first placed at r=4m and is then held fixed ? 2. Protons from a Van de Graaff accelerator are released from rest at a potential of 5 MV and travel through a vacuum to a region at zero potential. (a). Finad the final speed of the 5-MeV protons. (b). Find the accelerating electric field if the same potential change occurred uniformly over a distance of 2m 2. Relevant equations V=kq/r E= -dV/dx U=qV 3. The attempt at a solution 1. So I found that the electric potential at 4m is 4495 V and at infinity V=0. To find the work done, I have to integrate -Udx but I don't know what to put for the lower limit. Do I put infinity ? Or How do I do part b and c ? 2. So I found the speed in part a using energy equation and got 2.64 x 10^7 m/s How do I then do part b ? I know that E= -dV/dx but then I cannot solve this because I don't know dV.