Here's the question you clicked on:
brinethery
A neutron star has a constant density of 6 * 10^27 kg/m^3 and a mass five times that of our Sun. Compare its rotational inertia with that of the Earth (assume constant density). In both cases, the rotation axis is an axis through the center of the sphere.
@Mashy you know the density and the mass of the star. you can find the radius.
the ratio of the rotational inertia or the moment of inertia of star to the earth would be m1*(R1)^2/ m2*(R2)^2 m1 is five times the solar mass m2,R2 are the mass and radius of the earth R1 can be calcualted as follows 4/3pi(R1)^3 * d = m1 where d is the density
Thank you very much Diwakar. Yeah, I can see where you're going with that last calculation... just multiply volume of the sphere times the density, and volume cancels out, and the only variable left to solve for is r. Thanks so much!