I large,
? small
I small,
? large
(a)
(b)
?? 8.
8. (20 points) A figure skater with a mass of $M = 70 \text{ kg}$ is rotating 2 times
per second with her arms extended, as shown in Figure 8(a). When the skater
pulls her hands in, as shown in Figure 8(b), she rotates 6 times per second.
(i) In Figure 8(a), the distance from the skater's right hand to the axis of
rotation is $l = 1.4 \text{ m}$, and the mass of each arm is $m = 5 \text{ kg}$. The moments of
inertia for Figures 8(a) and 8(b) are given as $I_a = Mk^2 + \frac{ml^2}{2}$ and $I_b = Mk^2$,
respectively. Find the value of $k$.
(ii) Calculate the change in rotational kinetic energy from Figure 8(a) to Figure
8(b).
(iii) Why is there a difference in rotational kinetic energy between the two
cases?
