There are 2 questions that are giving a few of us problems. 1. Find the moment of inertia of a rod about an axis through its center if the mass per unit length is A=A*x A is linear density. This is a simple problem, but we are not sure how to use the given value for A (linear density). so far we have I=A * intergral of x^2 dx from 0 to L/2. which you finally get 1/12ML^2... 2. Same type of inertia problem except this is a disk about its center where mass density Q (which in normal cases is dm/dA) here Q=Q*r^(-1) Please help.