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**1. Homework Statement**

So I am going over some old problem as review. I have the solution to this problem and something is bothering me about it.

Here is the problem and solution:

what bothers me is this: When they are finding the expression for the kinetic energy of the disk, they use

*I*about its center 'A' and not about the hinge-point of the system 'O'.

The statement says that the "bar is welded at A"... and hence it cannot rotate about A. Angular velocity [itex]\omega[/itex] that they are using is of the

*bar*not the disk about its center.

Shouldn't the expression for the KE of disk use

*I*about A ?

EDIT:

I get this...the disk does not rotate, hence no KE (angular) ... but in the first version i think angular KE should be WRT point A

Here is the solution to the version where the disk is "pinned at A with a SMOOTH pin"...