If anyone could help me understand my professors answer for number 3.a on this link it would be greatly appreciated.

Question

anonymous · Answer

http://ftoddbaker.com/1211/problems/Ex3.html

anonymous · Answer

The question about the wheel. I want to say that E2=(.5(M+m)v^2) with is = to mgh. This is not what he has listed as the answer though.

anonymous · Answer

i dont think comparing potential energy of mass m with kinetic energy of disc is correct
moreover we have to note that the mass m is at rest(having zero kinetic energy)
to the maximum we can say that torque=I*omega
=I*V/R

no time was the disc displaced to any height so how can it have potential energy?