Rotating meterstick problem w/ weights.

[jrrodri7]

Homework Statement

Identical particles are placed at the 50-cm and 80-cm marks on a meter stick of negligible mass. This rigid body is then mounted so as to rotate about a pivot at the 0-cm mark on the meter stick. If this body is released from rest in a horizontal position, what is the angular speed of the meter stick as it swings through it's lowest position?

Homework Equations

Equations of rotational motion
torque = Fdsin(theta)
torque = I (alpha)
v = rw
(alpha) = A_c / r

The Attempt at a Solution

I used the different lengths in simultaneous equations to try and find the different omegas and add them together...but my answer had nothing to do with the question...

I then tried using parallel axis theorem and tried to plug in T = I(alpha) and such to figure out the real torque involved to find alpha and find w finally., and that produced no results...

 

[Hootenanny]

Homework Statement

Identical particles are placed at the 50-cm and 80-cm marks on a meter stick of negligible mass. This rigid body is then mounted so as to rotate about a pivot at the 0-cm mark on the meter stick. If this body is released from rest in a horizontal position, what is the angular speed of the meter stick as it swings through it's lowest position?

Homework Equations

Equations of rotational motion
torque = Fdsin(theta)
torque = I (alpha)
v = rw
(alpha) = A_c / r

The Attempt at a Solution

I used the different lengths in simultaneous equations to try and find the different omegas and add them together...but my answer had nothing to do with the question...

I then tried using parallel axis theorem and tried to plug in T = I(alpha) and such to figure out the real torque involved to find alpha and find w finally., and that produced no results...

Perhaps this problem would be better approached using conservation of energy.

 

[jrrodri7]

conservation of rotating object energy?hmmmm okay.

 

[Hootenanny]

conservation of rotating object energy?hmmmm okay.

Yes. You don't think that one can apply conservation of energy to rotating rigid bodies? Consider the potential and kinetic energy of the meter stick both when it is horizontal and vertical.