[问答题]
A person stands, hands at his siderk70ndw. 8ej3n) *y*hc uccr u, on z(o-o c* aiqsc(yo.(t v4n7tua platform that is rotating at a rate of 1.3rev/s If he raises his arms to a horizontal position, Fig. 8–48, z(iycntsuqo 4-oa .t7(v(co * the speed of rotation decreases to 0.8 $rev/s$ (a) Why? (b) By what factor has his moment of inertia changed?