For a thin planar ring of radius 'r' mm and thickness 't' mm, its radius of gyration about the polar axis (in mm) is:

According to the parallel axis theorem, the moment of inertia of a section about an axis parallel to the axis through its center of gravity IP is given by which of the following expressions? (Where A = area of the section, IG = moment of inertia of the section about an axis passing through its CG, and h = distance between the CG and the parallel axis.)

The moment of inertia of a hollow circular section, having external diameter D and internal diameter d, about its centroidal X-axis is given by: