1. The problem statement, all variables and given/known data http://img47.imageshack.us/img47/7206/wtffffftv0.th.jpg [Broken]http://g.imageshack.us/thpix.php [Broken] 2. Relevant equations Work is the dot product of force vector and displacement vector. Centripetal acceleration is velocity squared divided by radius -- multiply by mass to get force. 3. The attempt at a solution Parallel does no work, perpendicular speeds it up ----->>> which is wrong (failed this question). I understand that objects in circular orbit have zero acceleration and thus constant speed. But with elliptical orbits, the body is speeding up or slowing down depending on its position relative to the body exerting gravitational force upon it. What exactly is parallel to the planet itself? I'm having a hard time understanding how to apply force components when I don't know what the angles are.