Angular Velocity of u Shape - Solving for Angular Velocity

[Kelschul]

Angular Velocity?

A thin uniform rod is rotating at an angular velocity of 9.37 rad/s about an axis that is perpendicular to the rod at its center. As the figure indicates, the rod is hinged at two places, one-quarter of the length from each end. Without the aid of external torques, the rod suddenly assumes a "u" shape, with the arms of the "u" parallel to the rotation axis. What is the angular velocity of the rotating "u"?

Before: The system is a single rod of mass M and length L rotating about an axis through its center.
After: The system consists of three parts; a rod of mass M/2 and length L/2 rotating about an axis through its center and two masses M/4 rotating at a distance L/4 from the axis. (Treat these masses as particles.)



I know I should use the conservation of momentum, moment of inerta for the rod, Net torque= Inertia x angular acceleration but I have no idea where to start!

Help me exam tomorrow!

 

[Galileo]

Indeed, conservation of momentum is the way to go.
The momentum before is $I_1\omega_1$ and after it's $I_2\omega_2$.
So ask yourself what's given, what can you calculate and what is the unknown?