Question

The outstretched hands and arms of a figure skater preparing for a spin can be considered a slender rod pivoting about an axis through its center. When the skater's hands and arms are brought in and wrapped around his body to execute the spin, the hands and arms can be considered a thin-walled hollow cylinder. His hands and arms have a combined mass of 7.5 kg. When outstretched, they span 1.8 m; when wrapped, they form a cylinder of radius 25 cm.

The moment of inertia about the axis of rotation of the remainder of his body is constant and equal to 0.35 kg⋅m2 If the skater's original angular speed is 0.45 rev/s, what is his final angular speed?

Answer 1

Conservation of angular momentum can be applied since no external force is acting on the system( figure skater).

Moment of inertia of rod and moment of inertia of hollow cylinder (using parallel axis theorem) about axis of rotation is calculated and total moment of inertia in each case is calculated by adding the moment of inertia of remainder body.