# A simple rotational motion question

1. Sep 22, 2013

### nil1996

1. The problem statement, all variables and given/known data
A solid cylinder of mass M =1kg and radius 0.5m is pivoted at its centre and has three particles of mass m=0.1 mounted at its perimeter on the curved surface.The system is initially at rest.Find the angular speed of the cylinder,when it is swung through 900 in anticlockwise direction.
http://img24.imageshack.us/img24/3603/4ufn.png [Broken]
2. Relevant equations

3. The attempt at a solution
According to me it is impossible to find the angular velocity as the time taken to spin it in 900 is not given.So i think that the the question doesn't give complete information.Am i right??

Last edited by a moderator: May 6, 2017
2. Sep 22, 2013

### Simon Bridge

You are correct.

3. Sep 22, 2013

### nil1996

something clicked me right now.The cylinder is horizontal and the cylinder is rotating in anticlockwise direction due to the mass(which is exerting torque at the centre of cylinder) on the left of it.Now can we find the angular velocity when it is spun 90 degrees.

4. Sep 22, 2013

### nil1996

Yes sir i was wrong.By using energy conservation i found the answer.

5. Sep 22, 2013

### Simon Bridge

This statement is correct - as originally presented in post #1, the following information was not provided: that the cylinder is horizontal, held at rest, and then released so it is free to swing under gravity.

Well done for making the connection BTW.

Aside: When typing English, there is customarily a space after a the period at the end of a sentence. Also after other punctuation marks, see how I write? It makes the sentences easier to read.

6. Sep 22, 2013

### nil1996

i shall take care of it next time.

7. Sep 22, 2013

Thanks