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: Mass of Asteroid?

  1. Nov 21, 2004 #1
    Assume an asteroid's moon is 1.6 km wide, and 148 km from the center of the asteroid, which is 55 km long. The moon's orbit is circular with a period of 21 h.

    Whatis the mass of the asteroid?

    Ok This has to do with Kepler's Laws and I don't really understand Kepler's Law. I tried using the Law Of Periods so I did (75600 s)^2=((4pi^2)/(GM))*(148 km)^3. I get the wrong answer so I don't know what I did wrong. Any ideas?
     
  2. jcsd
  3. Nov 21, 2004 #2

    Doc Al

    User Avatar

    Staff: Mentor

    It's a circular orbit. Use what you know about centripetal acceleration and gravity.
     
  4. Nov 21, 2004 #3

    Doc Al

    User Avatar

    Staff: Mentor

    Of course there is nothing wrong with using Kepler's law! (Which is equivalent to what I suggested.) Be careful with units---convert km to m.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook