1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: A star that changed size

  1. Jan 15, 2010 #1
    1. The problem statement, all variables and given/known data

    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?

    2. Relevant equations

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

    3. 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

    the computer said that this answer is wrong and i don't know why
    Last edited: Jan 15, 2010
  2. jcsd
  3. Jan 15, 2010 #2


    User Avatar
    Homework Helper

    109.01 is not right. Try recalculating that number.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook