1. The problem statement, all variables and given/known data Comets travel around the sun in elliptical orbits with large eccentricities. If a comet has speed 1.5×104m/s when at a distance of 2.1×1011m from the center of the sun, what is its speed when at a distance of 5.1×1010 2. Relevant equations Conservation of energy 3. The attempt at a solution I was able to solve this using conservation of energy, but I was wondering why I don't the get same answer from conservation of angular momentum. There is no external force because the only force is the force of gravity, which is part of the system. Here is the attempt with conservation of angular momentum: m(r x v) = m(rfinal x vfinal) (r x v) = (rfinal x vfinal) The velocities are tangential so sin(90) = 1 (r)(v) = (rfinal) (vfinal) (1.5x104)(2.1x1011) = (5.1x1010)(vfinal) (vfinal) = 6.18 x 104 m/s The correct answer, obtained using conservation of energy is (vfinal) = 6.5 x 104 m/s The answers should be the same though. There is no external force or non-conservative forces.