The problem statement, all variables and given/known data A solid door of mass 39.30 kg is 2.34 m high, 1.68 m wide, and 3.23 cm thick. What is the moment of inertia of the door about the axis through its hinges? If the edge of the door has a tangential speed of 76.5 cm/s, what is the rotational kinetic energy of the door? The attempt at a solution I don't really know where to start. Should I find the center of mass of the door? Because I = Ʃmr^2? I know how to solve for the second half (Ek = (1/2)Iω^2), but I'm not sure how to calculate I.