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Homework Help: Orbit, and Centrifuge questions

  1. Oct 14, 2007 #1
    1. The problem statement, all variables and given/known data
    Communications satellites are placed in a circular orbit where they stay directly over a fixed point on the equator as the earth rotates. These are called geosynchronous orbits. The altitude of a geosynchronous orbit is 3.58 x10^7 m

    a)What is the period of a satellite in a geosynchronous orbit?
    b)Find the value of g at this altitude.
    c)What is the apparent weight of a 2000 kg satellite in a geosynchronous orbit?

    2. Relevant equations
    No Clue, I have never done this type of question.

    3. The attempt at a solution
    I was hoping someone could either guide me through this question or provide me with an example i could learn off.

    1. The problem statement, all variables and given/known data
    Astronauts use a centrifuge to simulate the acceleration of a rocket launch. The centrifuge takes 40.0 s to speed up from rest to its top speed of 1 rotation every 1.40 s. The astronaut is strapped into a seat 6.80 m from the axis.

    b)How many g's of acceleration does the astronaut experience when the device is rotating at top speed? Each 9.80 m/s^2 of acceleration is 1 g.

    2. Relevant equations
    not sure.. once again I've never done this type of question.

    3. The attempt at a solution
    Well for his tangential acceleration i got 0.763m/s^2 but from that I don't know how to get the g's of acceleration.
  2. jcsd
  3. Oct 14, 2007 #2


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    If the satellite stays over the same point on the earth, how many times does it orbit the earth in 24 hours?
  4. Oct 14, 2007 #3
    um it doesn't orbit earth.. whoops i mean 1. k but what about finding g?
    Last edited: Oct 14, 2007
  5. Oct 14, 2007 #4


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    And the "period" is the time it takes to complete one orbit! What is the period?

    The general formula for the force of gravity between to masses is [itex]GmM/r^2[/itex], here m is the mass of the satellite and M is the mass of the earth.
    Since F= mg, g =[/itex]GM/r^2[/itex]. You need to know: G, the mass of the earth, and the distance from the center of the earth to the satellite- that is the given altitude of the satellite plus the radius of the earth.

    You know, people on this forum, at least those likely to give you good hints, really love physics. Has it occured to you that calling yourself "iHate Physics" doesn't really encourage them to help you?
  6. Oct 14, 2007 #5
    really? i didn't think a name like that would be pretty serious around here. Sorry, if i offended you.
  7. Oct 14, 2007 #6
    for the apparent weight i used the formula wapp = mg(1+ay/g) g would be 0.223 but what would ay be?
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