A hollow cylindrical rod (rod 1) and a solid cylindrical rod (rod 2) are made of the same material. The two rods have the same length and the same outer radius. If the same compressional force is applied to each rod,

(a) Is the change in length of rod 1 greater than, less than, or equal to the change in length of rod 2?

(b) Choose the best explanation from among the following:

I. The solid rod has the larger effective cross-sectional area, since the empty part of the hollow rod doesn't resist compression. Therefore, the solid rod has the smaller change in length.

II. The rods have the same outer radius and hence the same crosssectional area. As a result, their change in length is the same.

III. The walls of the hollow rod are hard and resist compression more than the uniform material in the solid rod. Therefore the hollow rod has the smaller change in length?