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Quick physics help

  1. Oct 8, 2004 #1
    Quick physics help plz

    First off, i'm new to the board and want to say hi to everyone! I hope i can give and take from this site, i should be helpful in the chem forums, but physics is not my best. I have 2 quick questions if you could help me that'd be great.

    A space station is shaped like a ring and rotates to simulate gravity. If the radius of the space station is 120 m, at what frequency must it rotate so that it simulates Earth's gravity? [Hint: The apparent weight of the astronauts must be the same as their weight on Earth.] - in rev/s

    I did the following and got it wrong
    9.8 = V^2/120, found v = 34.29m/s
    34.29 / 2*pi*120 = .045 rev / s

    Where have i gone wrong?/

    A coin is placed on a record that is rotating at 33.3 rpm. If the coefficient of static friction between the coin and the record is 0.3, how far from the center of the record can the coin be placed without having it slip off?

    I'm plain lost on this one.
  2. jcsd
  3. Oct 8, 2004 #2


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    Looks okay to me. How do you know you're wrong ? Do you know what the answer should be ?

    How much force would you need to exert on a body to overcome friction, and cause it to slide? In the rest frame of the coin, this force would be provided by the centrifugal force. Remember, the linear velocity depends on the distance of the coin from the record center.

    PS : Welcome to PF. It's a great place to be ! :biggrin:
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