Question

9.An ice skater extends her arms as quickly turns on itself. Does your kinetic energy is conserved? Does your mechanical energy is conserved? Does your angular momentum is conserved? (Neglect friction in the range of time it takes to extend the arms.) If any of these magnitudes is not retained say whether increases or decreases.

Answer 1

Kinetic energy is conserved in this process because it is quickly turn on by reducing pressure of air.

Same, mechanical enegy is also conserved.

Like linear momentum (mv), angular momentum (r×mv) is a conserved quantity, where rr is the vector from the center of rotation. For a skater holding a static pose, for each particle making up her body, the contribution in magnitude to the total angular momentum is given by mvr. Thus bringing in her arms reduces r for those particles. In order to conserve angular momentum, there is then an increase in the angular velocity.