## angular momentum question

ok the question is a spherical star expands to 6 times its volume but its mass remains constant and is uniformly distributed - how does the period of rotation change?

obviously it rotates slower and thus the period goes up, but i dont know how to solve it mathematically. can someone give me some pointers and get me going in the right direction? is there a main equation i should be using and do i need to find the ratio of the radii before and after the star expands?

thanks.
 PhysOrg.com science news on PhysOrg.com >> Leading 3-D printer firms to merge in $403M deal (Update)>> LA to give every student an iPad;$30M order>> CIA faulted for choosing Amazon over IBM on cloud contract
 Mentor Blog Entries: 1 Hint: What's conserved? How does the rotational inertia change when the star expands? (Yes, you'll need to know how the radius changes.)
 angular momentum is conserved. and rotational inertia increases as the star expands, hence the angular velocity will go down to conserve angular momentum (L=Iw), right? and if the volume goes up by 6 times, it means the radius went up by ~1.8 times. do i then square that value because I=mr^2? which means the inertia went up by (1.8)^2 = 3.3 and therefore the angular velocity (w) went down by 3.3 to compensate for that? am i understanding this correctly?

Mentor
Blog Entries: 1

## angular momentum question

Sounds like you have the right idea!

$$I = 2/5 m r^2$$

$$r_2 = 6^{1/3}r_1$$

$$I_2 = 6^{2/3}I_1$$

Recognitions:
Gold Member
Homework Help