Ballet A ballet student with her arms and a leg extended spi

Ballet A ballet student with her arms and a leg extended spins with an initial rotational speed of 1.0 rev/s. As she draws her arms and leg in toward her body, her rotational inertia becomes 0.80 kg middot m^2 and her rotational velocity is 4.0 rev/s. Determine her initial rotational inertia.

Solution

I_f = 0.80 kg.m² , w_f = 4.0 rev/s

I_i w_i = I_f w_f

I_i =  I_f w_f / w_i

= (0.80 * 4.0) / (1.0)

Initial rotational inertia = 3.2 kg.m²