Question

The four masses shown in the figure(Figure 1) are connected by massless, rigid rods. Assume that m=250g. Find the moment of inertia about an axis that passes through mass A and is perpendicular to the plane of the image http://imageshack.us/content_round.php?page=done&l=img803/3633/12ex14.png

Answer 1

I can't see your image

Answer 2

The moment of inertial for a number of point masses that lie in the plane perpendicular to the axis of rotation is
\[ I = \sum_{i=1}^N m_i r_i^2\]
Where ri is the distance from mass i to the axis of rotation in that plane. So, take each mass and multiply it by the distance from the axis squared, and add these all together.