[问答题]
A person stands, hands at his side, on a platforxtpv4fmm;mem ,+(q 9r,2sw*h 1va bhbm that is rotating1 wt 4v3akdvh9 at a rate of 1.3rev/s If he raises his arms to a horizontal position, Fig. 8–48, the speehdvtv1k 34w9 ad of rotation decreases to 0.8 $rev/s$ (a) Why? (b) By what factor has his moment of inertia changed?