Potentials of charges in code

You will write three functions about point charges. They use $V = kq/r$ and $U = kq_1q_2/r$.

The idea. Each charge is given as (q, x, y), with the charge in C and the position in m. The potential at a point is the sum of the potentials of all the charges. The energy of a group is the sum over every pair.

Your tasks.

1. In potential, return the potential in V at a distance r from a point charge q.
2. In potential_at, return the total potential in V at the point (px, py) from every charge in the list.
3. In group_energy, return the potential energy of the whole group in J. Count each pair once.