Question

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Answer 1

Suppose a star the size of our Sun, but with mass 4.0 times as great, were rotating at a speed of 1.0 revolution every 5.0 days. If it were to undergo gravitational collapse to a neutron star of radius 15km , losing three-quarters of its mass in the process, what would its rotation speed be? Assume that the star is a uniform sphere at all times, and that the lost mass carries off no angular momentum

Answer 2

angular momemtum conservation
mw=const.
so 4m*(1/5)=m*w +3m*0
w=4/5 i.e. 4.0 revolution every 5.0 days.