A skater has a moment of inertia of 5 kg-m² when her arms are outstretched and 2 kg-m²?

Question

A skater has a moment of inertia of 5 kg-m² when her arms are outstretched and 2 kg-m² when they are later brought to her sides. If she starts spinning at 3 radians/s, what is her final angular speed?

Answer 1

Angular momentum L is
L=Iw where
I - moment of inertia
w- angular velocity

Since angular momentum is conceved

L1=L2

I1w1=I2w2
w2= (I1/I2)w1
w2=(5/2)3=7.5 rad/s