1. The problem statement, all variables and given/known data A particle of mass "m" and electric charge "q" moves without friction along an ellipse in the horizontal plane, in the presence of a constant electric field of intensity E directed along the large semiaxis of the ellipse. Write the Lagrange function 2. Relevant equations We now, obviously the ellipse equation so we choose as general coordinates: X1 = a*cos(phi) X2 = b*sin(phi) 3. The attempt at a solution L = T - U; T = m/2*(X1'squared + X2' squared) But U?