Question

A ballet student with her arms and a leg extended spins with an initial rotational speed of 0.90rev/s . As she draws her arms and leg in toward her body, her rotational inertia becomes 0.80 kg⋅m2 and her rotational velocity is 4.1rev/s .
Determine her initial rotational inertia.

Answer 1

Initial inertia = 3.6 kg . m^2

final inertia = 0.80 kg.m^2rotational velocity final = 4.1 rev/s
rotational velocity initial = 0.90 rev/s 
lo= lf(final inertia) *  Wf(rotational velocity final)/ Wo (rotational velocity initial)

lo =  0.8*4.1 / 0.90 = 3.6 kg m2