A 50 kg student holds a 2.0 kg mass in each hand and is sitting on a stool that

Question

A 50 kg student holds a 2.0 kg mass in each hand and is sitting on a stool that can rotate freely about a vertical axis. With the masses held at arm's length the student is set spinning at 1.2 revolutions per second. While spinning, the student draws their arms in, holding the masses to their chest. Using the principles of rotational motion that you learned in PHYSI40.explain how their rotational motion changes as they draw their arms in. As the student draws their arms in, does their kinetic energy increase, decrease, or stay the same? Justify your answer.

Explanation / Answer

(i) Ans-

As the student draws his arm in the moment of inertia of the system will decrease as I=mr2 so since r will decrease therefore the mment of inertia of the system will also decrease.

Now by conservation of angular momentum since inertia is decreasing the angular speed of the system will increase.

(ii) Ans-

KE= 1/2 *I*w2

since I*w is constant and w is increasing so the net kinetic energy of the system will increase.

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