[问答题]
A person stands, hand qb/ uwcu.ab7a 5ts- yz(ew c-e.kxm/)s au)j tyfgyf-96t his side, on a platform that is rotating at a rate of 1.3rev/s If he raises his arms to a horizontal position, Fig. 8–48, the sp yfj-) u9ftg6yeed of rotation decreases to 0.8 $rev/s$ (a) Why? (b) By what factor has his moment of inertia changed?