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: Gravity & Orbits Problem?

  1. Oct 18, 2009 #1
    1. The problem statement, all variables and given/known data

    Mostly a bunch of extraneous information, so feel free to skim:

    Large stars can explode as they finish burning their nuclear fuel, causing a "supernova". The explosion blows away the outer layers of the star. According to Newton's third law, the forces that push the outer layers away have reaction forces that are inwardly directed on the core of the star. These forces compress the core and can cause the core to undergo a "gravitational collapse". The gravitational forces keep pulling all the matter together tighter and tighter, crushing atoms out of existence. Under these extreme conditions, the protons and electrons can be squeezed together to form a neutron. If the collapse is halted when the neutrons all come into contact with each other, the result is an object called a neutron star, an entire star consisting of solid nuclear matter. Many neutron stars rotate about their axis with a period of 1 s and, as they do so, send out a pulse of electromagnetic waves once a second. These stars were discovered in the 1960s and are called pulsars.
    Consider a neutron star with a mass equal to the sun, a radius of 13 km, and a rotation period of 1.2 s.

    2. Relevant equations/Attempt at solution

    I'm not sure, but I used T^2 = (4pi^2/GM)r^3. G = 6.67e-11, M of sun = 1.98892e30... Perhaps I'm not putting the right value for T? I've tried 365x24x60x60 since it was geosynchronous...

    Here is other information I calculated that might help:
    Speed of a point on equator of star: 68067.84 s
    g on surface of neutron star: 7.8497611e11
  2. jcsd
  3. Oct 18, 2009 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    What exactly are you trying to find? You never really say.
  4. Oct 18, 2009 #3
    Oh, sorry. The question was: what is the radius of a satellite around the neutron star with and geosynchronous orbit.

    UPDATE: I've figured it out. All I had to do was use a different formula.

    Thanks for help though.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook