I take it that the idea for part 6 is that a non-rotating rectangular bar is dropped onto the rotating disk, but initially does not notate with it (why not?). Then (not by friction or eany other simple coupling I can imagine where the torque on the bar would typically be proportional to the angular velocity difference, but by some other unstated mechanism,) the rod is angularly accelerated with constant torque (weird no?), somehow coupling to and using the rotational energy of the disk, and that frictional energy losses can nevertheless be neglected. No wonder our student was confused. This is a rather unphysical or unusual situation, no? What might be a mechanism to do this? Does anyone else find this difficult to visualize as an actual situation? To me, at a minimum, little more clarity and detail in the initial description of the problem might have been helpful for our student's initial visualization.