[问答题]
A person stands, hands at his ss3ar1-gqv2 he ide, on a platform that is rotating at a rat f6zog t6(rf k)u:;tlne of 1.3rev/s If he raises his arms to a horizontal position, Fig. 8–4 n6 lz):(kf;ftu tr6go8, the speed of rotation decreases to 0.8 $rev/s$ (a) Why? (b) By what factor has his moment of inertia changed?