A star that changed size

  • #1

Homework Statement



A star of mass 1.81×1031 kg and diameter 8.10E+9 m rotates with a period of 25.0 days. Suddenly the star changes size, and rotates with a new period of 18.0 days. Assuming a uniform density both before and after the size change, what is the new diameter of the star?



Homework Equations



Volume = 4/3*3.14*R^3
Density = M / VOL
I =2/5*M*R^2

The Attempt at a Solution



R(initial) = 8.10*10^9/2=4.05*0^9
Volume(initial) = 4/3*3.14*(4.05*10^9)^3=2.782*10^29
Density= (1.81*10^31/(2.782*10^29)=65.061
I(initial)=2/5*(1.81*10^31)*(4.05*10^9)^2=1.187*10^50
I(final)=2/5*65.061*4/3*3.14*Rf^3*Rf^2=109.01Rf^5
I(initial)*W(initial)=I(final)*W(final)
1.187*10^50*(2*3.14/25)=109.01*(2*3.14/18)*R(final)^5
R(final)^5=1.187*10^50*(2*3.14/25)/(109.01*[2*3.14/18])
R=(2.983*10^49/38.051)*10^(-5)=3.792*10^9
K=2R=7.58*10^9

the computer said that this answer is wrong and i don't know why
 
Last edited:

Answers and Replies

  • #2
ideasrule
Homework Helper
2,271
0
I(final)=2/5*65.061*4/3*3.14*Rf^3*Rf^2=109.01Rf^5

109.01 is not right. Try recalculating that number.
 

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