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7) An Ice skater with her arms extended is rotating with initial kinetic energy Eki and has a moment of inertia I, then when she pulls her arms close to her body her moment of inertia goes down to 0.25 I. The final total kinetic energy (Ekf ) of the skater is A. Eki B. 2Eki C. 4Eki D. 16Eki E. Eki/4

Respuesta :

Answer:

C. 4Eki

Explanation:

The kinetic energy due to the rotation is:

[tex]K = \frac{1}{2}\cdot I \cdot \omega^{2}[/tex]

The motion of the ice skater is modelled after the Principle of Angular Momentum Conservation:

[tex]I_{o}\cdot \omega_{o} = I_{f}\cdot \omega_{f}[/tex]

The initial angular speed is:

[tex]\omega_{o} = \sqrt{\frac{2\cdot E_{ki}}{I} }[/tex]

The final angular speed is:

[tex]\omega_{f} = \frac{I_{o}}{I_{f}}\cdot \omega_{o}[/tex]

[tex]\omega_{f} = 4\cdot \sqrt{\frac{2\cdot E_{ki}}{I} }[/tex]

The final kinetic energy is:

[tex]K = \frac{1}{2}\cdot \left(\frac{1}{4}\cdot I \right)\cdot \left(\frac{32\cdot E_{ki}}{I} \right)[/tex]

[tex]K = 4\cdot E_{ki}[/tex]

The correct answer is option C.