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: Law of Gravitation

  1. Nov 27, 2005 #1
    Satellite A has a mass of 1000kg. Satellite B has a mass of 2000kg. BOth are in orbit 250km above the surface of the earth. Satellite A will have an orbital speed that is ____ satellite B.

    1. the same as.
    2. four times that of.
    3. twice that of.

    Not really sure on this. I originally said half that of and it was incorrect.

    The gravitational force between two masses is 36 N. If the distance between the mass is decreased to one-half its original value, the force of gravity will be:

    1. 144 N
    2. 9 N
    3. 18 N

    My original answer was 72 N, and I forgot to square the radius if I remember correctly. So I am fairly confident the answer is 144 N.

  2. jcsd
  3. Nov 27, 2005 #2

    Physics Monkey

    User Avatar
    Science Advisor
    Homework Helper

    A hint for your first question: does the trajectory of a particle in a given gravitational field depend on its mass? In other words, if a satellite is moving around the Earth at a given radius in a circular orbit, does its speed depend on its mass?

    A hint for your second question: the gravitational force is inversely proportional to the square of the distance.
  4. Nov 27, 2005 #3
    Very Briefly, cos Ive gotta go in a minute.
    [tex]F_g = \frac{GM_eM}{r^2}[/tex]
    [tex]F_c = \frac{Mv^2}{r}[/tex]
    [tex]v = \sqrt{\frac{GM_e}{r}}[/tex]
    Where M_e is the mass of the earth, and M is the mass of the object in orbit, so the velocity of the two will be the same as long as the radius of orbit is the same.:wink:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook