Alright I'm really stuck on this question. I was wondering if anyone could help:
(a) Show that the total energy (per unit mass) of a particle orbiting in an attractive Keplerian potential V(r) = -GM/r is
E = (1/2)(dr/dt)^2 + (1/2)(J^2/r^2)-(GM)/r
where J = |r x v| is the particle's angular...