Understanding Angular Momentum & Energy in Rotational Motion

[Ali Asadullah]

Suppose a man is holding his arms extended in with some masses in each hand. He is set rotating about a vertical axis . If he pulls his hands toward his stomach then according to law of conservation of angular momentum there is an increase in his angular velocity. Also there is a change in his KE from where the energy comes or go? Also We have work=Change in KE
which force does work in dis case?

 

[Ali Asadullah]

Actually this is question in University Physics H D Young 10 edition Example 10-13.

 

[Doc Al]

What force do you think does work in this case? Where do you think the energy comes from?

 

[Ali Asadullah]

Dear i don't know that is why iam asking from u people.

 

[rock.freak667]

Dear i don't know that is why iam asking from u people.

How would he decrease his moment of inertia in this case?

 

[Ali Asadullah]

Dear moment ov inertia is mr^2, when he pulls his hands towards his stomach r^2 decreases and hence Moment ov inertia decreases.

 

[Ali Asadullah]

I have asked ma Physics teacher and he replied that the force with which he pulls his hands towards his body actully does work.
Soory for any Grammatical mistake as English is not ma mother tongue.

 

[Doc Al]

I have asked ma Physics teacher and he replied that the force with which he pulls his hands towards his body actully does work.

Absolutely.