# Moment of inertia for rectangular plate

by siestrand
Tags: inertia, moment, plate, rectangular
 P: 3 Hi! I've got a problem with this: Count moment of inertia for rectangular plate a x b, if you know that moment of inertia of thin rod is $$\frac{1}{12}ml^2$$. Do not use integrals!, others mathematical functions required (I can proof this moment by integrals, but this is not issue). I know that I have to use Steiner theory, but how? No integrals? :( Please help.
 P: 3 There is one mistake, I think. One slice has of course $$I = m(a^2)/(12n)$$ but not by this axis! the axis is in the centre of plate and every slice has $$I = m(a^2)/(12n) + \frac{m}{n} * r^2$$ from Steiner theory when r ist distance from axis.