Rotational Energy and Kinetic Energy

[madhuparc2004]

Homework Statement

[PLAIN]http://img189.imageshack.us/img189/5994/energyq.png

Homework Equations

This is a question by Monash University...i need to do part b by Energy conservation equations...but i don;t get the answer from that..
pleasez tell me how to do part b by Energy conservation equations...
thank u

The Attempt at a Solution

 

[Mindscrape]

Do you know how to set up a Lagrangian?

 

[madhuparc2004]

Do you know how to set up a Lagrangian?

no whts that?

 

[madhuparc2004]

y is no body helping me?