Jump to content
Science Forums

Rotation problem


Recommended Posts

A rotating sphere contract slowly due to internal forces to (1/n)th of its original radius.What happens to its angular velocity.Show that increase in its energy equals the work done during its contraction.

 

(2/5)MR^2*w_1=(2/5)M(R/n)^2*w_2

 

From this we should find the change in w.

Regarding the workdone: Please help me to start with.

Link to comment
Share on other sites

Well, what you have here is:

 

[math]\frac25 MR^2 w_1=\frac25 M(\frac{R}{n})^2 w_2[/math]

 

Can you see how the moment of inertia, [math]\norm\frac25 MR^2[/math], changes? Write the new one in terms of n and the old one and you should be able to get it.

Link to comment
Share on other sites

Obviously the work must be equal to the change in kinetic energy, therefore the integral of centrifugal forces in dr must equal the difference.

 

Perhaps your difficulty is due to asking about potential energy. Yep, that requires a spot of careful thinking.... :)

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...