1. The problem statement, all variables and given/known data A ball is going around in a circle of radius 5 m. It starts from rest, and goes through an angle change of 26 rad in 5 seconds. The ball weighs 0.3 kg. Find its moment of inertia, and find the torque about the origin. 2. Relevant equations 3. The attempt at a solution What I'm doing seems too simple, so I bet it's wrong... I thought moment of inertia was just mass times radius2. My textbook doesn't give it for this situation but it gives the moment of inertia for other shapes, all of which are this but multiplied by some factor. And I think the torque would be zero because the force acting on the ball would be towards the center of the circle, and since torque is r x F, and F is 180 to r, rFsin(180) = 0.