Hi all, I'm working on a catapult for a project and I'm having some problems with some of the calculations, I'm trying to get the angular velocity of my catapult's arm by first obtaining the torque and moment of inertia. 1. The problem statement, all variables and given/known data http://img46.imageshack.us/img46/2687/physproblem.th.png [Broken] A diagram I made with all the information and the sum of torques solved. 2. Relevant equations Torque = Force * Distance to axis of rotation I=(1/12)ML^2 + MD^2 F = mg 3.Attempt at solution I've solved Torque, but I have some doubts for Moment of Inertia: 1) Is M the mass of the arm by itself or the addition of all the masses involved (arm+counterweight+basket+projectile) 2) Is L the distance of the whole Arm and D the distance of the axis of rotation to the center of mass? I=(1/12)ML^2 + MD^2 I=(1/12)(0.9)(.3650)^2 + (0.9)(.1)^2 I=.0189 kg*m^2 Is this right?