I need some serious help for finding the angular frequency of this system The 3.81 kg cube has edge lengths d = 5.40 cm and is mounted on an axle through its center. A spring (k = 1100 N/m) connects the cube's upper corner to a rigid wall. Initially the spring is at its rest length. If the cube is rotated 3.00° and released, what is the period of the resulting SHM? Here's a picture to help.. http://farm3.static.flickr.com/2108/2077... solution: From the ref, the moment of inertia I of a rectangular prism is m*(a^2+b^2)/12; for a cube with side d, I = md^2/6. At a distance r from the center the effective mass I/r^2 = (m/6)*d^2/r^2; since d/r = sqrt(0.5) it's m/12. Then ω^2 = k/(m/12). Since 3 deg is a small angle we can ignore the variation of r with rotation. question: i m just confused where the 12 came from???