A skater is initially spinning at a rate of 15 rad/s with a rotational inertia of 2.78 kg·m2 when her arms are extended. What is her angular velocity after she pulls her arms in and reduces her rotational inertia to 1.65 kg·m2? I have so much trouble with these problems because I haven't a clue where to begin. I know that rotational inertia = http://library.thinkquest.org/16600/advanced/5-7.gif.[/URL] Angular velocity is [PLAIN]http://hyperphysics.phy-astr.gsu.edu/hbase/imgmec/avel3.gif.[/URL] [Broken] Knowing this, how can I derive the the new angular velocity?