Question on Rotational Dynamics

[alamin]

1.A uniform Disc of Radius R is rotating in its own plane with angular velocity w when it is placed flat on a rough table. If u the coefficient of sliding friction is independent of velocity show that the time taken for the disc to come to rest is
(3RW)/(4ug). How does the kinetic energy of rotation of the disc vary with time?

 

[stunner5000pt]

ok please show us what work you have done. we arent going to solve (although we can) your problems for you
also for your problems remember that
$$\Delta K + \Delta U = W_{friction}$$
where K represnets kinetic energy
U represnts potential energy
and W represents work
and delta is the change

 

[Harmony]

May I know what is the formula to calculate work done by frcition? Displacement is given in the case, but the friction force is not.

 

[stunner5000pt]

work done is F d cos(angle)
if angular then d = (angular displacement)

 

[Psi-String]

work done is F d cos(angle)
if angular then d = (angular displacement)

I thought the work done by the friction force is $$\int \vec{\tau} \cdot d\vec{\theta}$$?

 

[quantumdude]

Psi-String,

We appreciate that you are willing to assist, but please do not offer complete solutions to homework questions.

Just to remind everyone, the Homework Help section of the PF Global Guidelines says the following:

On helping with questions: Any and all assistance given to homework assignments or textbook style exercises should be given only after the questioner has shown some effort in solving the problem. If no attempt is made then the questioner should be asked to provide one before any assistance is given. Under no circumstances should complete solutions be provided to a questioner, whether or not an attempt has been made.[/color]