Question

A physics teacher sits on a stool that is free to rotate nearly without friction about vertical axis. He outstretched hands each hold a large mass so that the rotational inertia is 12 kgm . By pulling his arms close to his body he is able to reduce moment of inertia to 6kgm. If he starts spinning at 0.5rad/s, what is his speed after she draws his arms in?

Answer 1

Answer:

His speed after he draw his arms inside will be 1 rad/s

Explanation:

As we know that there is no external torque on the system of mass and the person so we can say that angular momentum of the system will remain conserved

So here we can say that

$I_1\omega_1 = I_2\omega_2$

here we have

$I_1 = 12 kg m^2$

$I_2 = 6 kg m^2$

$\omega_1 = 0.5 rad/s$

now we have

$12 \times 0.5 = 6 \times \omega$

$\omega = 1 rad/s$

So his speed will be 1 rad/s

#Learn

Topic : Angular momentum conservation

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