# A simple rotational motion question

nil1996

## Homework Statement

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]

## 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??

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Homework Helper
You are correct.

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.

nil1996
Yes sir i was wrong.By using energy conservation i found the answer.

Homework Helper
nil1996 said:
i think that the the question doesn't give complete information.Am i right??
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.

nil1996
i shall take care of it next time.

nil1996
Thanks