The following things may clarify the homework:
on problem 8.75, there isn't necessarily a right or wrong answer to the second part. You can neglect air resistance, and assume that whichever shape accelerates the fastest from rest will win the race. on problem 8.79, you can assume that the body is like a rod of length l for purposes of mass distribution. This won't give you the exact answer for part (a) -> apparently you get this answer if you assume Izz=0, or at least that's what I got. Also keep in mind that the person 'rolls' on the floor, so you know the accel of the center of the foot.. For part (b) you want to find solutions to the differential equation that do not grow very large as time gets large.
In 8.79, you can assume that the cm of the person is at G, which is a distance L/2 from the ground if the person is standing up straight (phi=0).