Hi, This is the statement of the problem of AP French's textbook "Newtonian Mechanics". 1. The problem statement, all variables and given/known data The commander of a spaceship that has shut down its engines and is coasting near a strange-appearing gas cloud notes that the ship is following a circular path that will lead directly into the cloud (see the figure). He also deduces from the ship's motion that its angular momentum with respect to the cloud is not changing. What attractive (central) force could account for such an orbit? (ANSWER : F ~ -1 / r^5) 2. Relevant equations 3. The attempt at a solution From the information given, angular momentum = m * r^2 * (dtheta / dt) = constant. The acceleration of the ship is a combination of tangential and radial acceleration, the resultant of which is along the line joining the spacecraft and the cloud. I don't know where to proceed from here. Thank you very much for your help.