## On average, both arms and hands together account for 13 % of a person’s mass, while the head is 7.0% and the trunk and legs account for 80

On average, both arms and hands together account for 13 % of a person’s mass, while the head is 7.0% and the trunk and legs account for 80 % . We can model a spinning skater with her arms outstretched as a vertical cylinder (head, trunk, and legs) with two solid uniform rods (arms and hands) extended horizontally. Suppose a 61.0-kg skater is 1.80 m tall, has arms that are each 70.0 cm long (including the hands), and a trunk that can be modeled as being 35.0 cm in diameter. The skater is initially spinning at 70.0 rpm with his arms outstretched.

Required:

What will his angular velocity be (in rpm) when he pulls in his arms until they are at his sides parallel to his trunk?

## Answers ( )

Answer:Explanation:The expression for the moment of inertia of the person is:

Arms outstretchedArms parallel to the trunkThe final angular speed is found by means of the Principle of Angular Momentum Conservation: