A student sitting on a stool that is free to rotate but is initially at rest, holds a bicycle wheel. The wheel has a rotational velocity of 5 rev/s about a vertical axis, as shown in the diagram. The rotational inertia of the wheel is 2 kg·m² about its center and the rotational inertia of the student and wheel and platform about the rotational axis of the platform is 6 kg·m².
a. What are the magnitude and direction of the initial angular momentum of the system?
b. If the student flips the axis of the wheel, reversing the direction of its angular-momentum vector, what is the rotational velocity (magnitude and direction) of the student and the stool about their axis after the wheel is flipped? (fig. 8.23.) 

c. Where does the torque come from that accelerates the student and the stool? Explain. 

SP4 Diagram