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Homework Help: Period of moving object

  1. Oct 5, 2008 #1
    1. The problem statement, all variables and given/known data

    The rings of a Saturn-like planet are composed of chunks of ice that orbit the planet. The inner radius of the rings is 170,000 km. The mass of this planet is 5.7x10^26 kg.
    Find the period of an orbiting chunk of ice at the inner radius.

    2. Relevant equations

    The force of gravity on the Saturn-like planet:
    g=(G)(Mass of planet)/(radius squared)
    Centripical velocity (can I do this using g from above as a?):
    a=(squared V)/r
    Then, use value of calculated v:
    V=(2)(3.14)(r)/(T) to find T

    3. The attempt at a solution

    I was able to calculate g, and used the above equations:
    g=a (centripical)
    1.3156m=(squared v)/(1.7x10^8m)

    The correct answer is 2x10^4s.
  2. jcsd
  3. Oct 5, 2008 #2
    Can someone please help me? Please I did really try to get it on my own but I just don't understand where to go after calculating the gravity. How do I relate gravity with period?
  4. Oct 6, 2008 #3
    Okay, so I did a little work on my own again and am still stuck. I derived the force by setting F=G*m1*m2/r^2 and plugging in the values:
    r=7.8e7 (in meters)

    Then I set that answer equal to m*a, from F=ma, and used the m1 value from above to get a velocity of 8.167e-6m/s. Not the right answer.
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