# Period of the sun

1. Nov 14, 2004

### wildrjetta

Could someone help me start this problem. My mind it in the angular momentum mode and I am having trouble seeing where to start on this one.

The sun's radius is 6.96E8m and it rotates with a period of 25.3d. Estimate the new period of rotation of the sun if it collapses with no loss of mass to become a neutron star of radius 5.5km. Give the result in seconds.

Thank you very much!

2. Nov 14, 2004

### CartoonKid

With the given radius you can find $$I_{initial}$$ and $$I_{final}$$. With the given period, find out $$\omega_{initial}$$. Then you use conservation of angular momentum to achieve your answer.

3. Nov 14, 2004

### Phymath

as such...(you don't need the moments of inertia exactly because it maintains a spherical shape and same mass so those factor out)

$$(r_i)^2 \omega_i = (r_f)^2 \omega_f$$
$$\omega_f = \frac{(r_i)^2 \omega_i}{(r_f)^2}$$
$$T_{new} = \frac{2 \pi}{\omega_f}$$

4. Nov 14, 2004

### wildrjetta

I calculated two different answers, both of which were to my dismay incorrect....but I am thinking that a conversion error might be the culprit. I am having trouble understanding what "a period of 25.3d" is -- as in, what does "d" stand for....should it be a time unit?

5. Nov 14, 2004

### cougar_21

in a period d=days

6. Nov 14, 2004

### wildrjetta

THANK YOU THANK YOU THANK YOU!!! to everyone involved in helping with this problem!!