Physics pls anyone can help me? its urgent
posted by rosan .
Four charges are arranged at the corners of a regular tetrahedron (a pyramid with four sides that are identical equilateral triangles). The charges are 1 Coulomb each, and the sides of the tetrahedron are all 1 meter. How much energy in Joules is required to assemble this arrangement of charge

Simple. What is the Potential energy of each charge? Well, PE is a scalar, so the distances are the same to each charge, so
energy=k(q1Q2/r+Q1Q3/r+Q1Q4/r+Q2Q3/r+Q2Q4/r+Q3Q4/r)= 6k if all q are 1, all r is 1.
Now consider putting the thing together.
first charge, no energy
second charge, energy= kQq/r=k
third charge, energy= 2k
fourth charge, energy=3k
total work: 6k 
what is k?