Work Energy Theorem and Uniform Disc Problem

[theBEAST]

Homework Statement

Using work energy theorem, solve:

The Attempt at a Solution

The actual answer (3.11s) is exactly half of my answer. Does anyone know what I did wrong?

 

[grzz]

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$^{2}$.

 

[theBEAST]

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.

 

[haruspex]

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.