Rotational Dynamics, 1.68(SS.Krotov) and 1.264(Irodov)

[Shridhar]

Homework Statement

I have attatched both the problems. The figure is essentially the same.

Homework Equations

1. Energy conservation
2.mgcosx - N = mv^2/r , where N is zero in limiting case.

The Attempt at a Solution

I solved the whole question and got the answer given in irodov(0.33 gR(7cosx-4))^1/2 .
But answer given in krotov is different.
So, there must be a difference in questions but i am unable to grasp it.
Thanks in advance.

 

[haruspex]

there must be a difference in questions

The moments of inertia are different.

 

[Shridhar]

The moments of inertia are different.

Well, in the detailed answer Krotov has ignored Kinetic energy due to rotational motion completely.His final equation is
mv^2/2 = mV^2/2 - mgr(1-cosx).
Anyways, moment of inertia of solid cylinder and disk are same

 

[haruspex]

moment of inertia of solid cylinder and disk are same

In https://www.physicsforums.com/attachments/15531967174434896316018851325402-jpg.240611/ it is light (read, massless) wheels on a thin heavy axle. So negligible rotational KE about the mass centre.