I have this question: A particle of mass m moves under the influence of a central force; F = -grad (V) where V(r) is the potential energy. Angular momentum is conserved because the force is central. The constants of motion are L and energy E. We use polar coordinates r(t) and θ(t) to describe the motion. Derive an equation for dr/dθ as a function of r. [The solution of this first-order differential equation determines the orbit.] Does anyone know how to do this? Thanks!