Work Energy Theorem and Uniform Disc Problem

AI Thread Summary
The discussion focuses on applying the work-energy theorem to a problem involving a uniform disc. The participant's calculated answer of 3.11 seconds is noted to be half of the expected result. It is confirmed that the moment of inertia used, \(\frac{1}{2}MR^{2}\), is correct. The issue seems to stem from not accounting for two factors of 1/2 in the kinetic energy calculation. Clarification on the proper application of the theorem is sought to resolve the discrepancy.
theBEAST
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Homework Statement


Using work energy theorem, solve:
9rA7A.png

The Attempt at a Solution


The actual answer (3.11s) is exactly half of my answer. Does anyone know what I did wrong?
SFjXx.jpg
 
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Note that moment of inertia of a uniform disc about an axis through its centre and perpendicular to its plane is

\frac{1}{2}MR^{2}.
 
grzz said:
Note that moment of inertia of a uniform disc about an axis through its centre and perpendicular to its plane is

\frac{1}{2}MR^{2}.

Yup! That is what I used I believe.
 
theBEAST said:
Yup! That is what I used I believe.
There should be two factors of 1/2 - one from Iω2/2 for the KE and another from I=Mr2/2.
 

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