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Centripetal Force Question need help immediately

  1. Oct 28, 2006 #1
    There is a guy a ride. The combined mass of the man and the swing is 200kg and the legnth of the string the pulls him around in a circle is. 12.0m the string makes an angle of 65 degrees. Find the force that moves him in this circular motion and find the speed he is moving at.

    I am kind of lost since I do not know how to find the period or anything. This is a A.P. Physics class in highschool without the use of calculus.
  2. jcsd
  3. Oct 28, 2006 #2


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    You need to find the tension in the rope.

    The vertical component of th tension balances the weight, so you should be able to calculate it since you know the angle.

    The find the horizontal compt of the tension. This provides the centripetal force. Then, use trig to find r, and then the formula for centripetal force should give you the speed.
  4. Oct 28, 2006 #3
    I really still do not understand the question so your saying the tension is provided by 12msin65? that would the magnitude of the vertical component?
  5. Oct 28, 2006 #4


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    Well, I don't know for sure whether its cos65 or sin 65 since you didn't say whether the angle of 65 is with the vertical or horizontal......

    And the 12 has nothing to do with it. 12 is a length, not a force - be careful
  6. Oct 28, 2006 #5
    i know that but doesn't the tension provide the centripetal force? wouldnt it be T=Fc=mv^2/r? but the problem is we don't know v so i am not sure how to find Fc? how do i find the force that provides it without knowing the period even if we know the components of the string? I don't believe hte components of the string have anything to do with it.
  7. Oct 28, 2006 #6

    Doc Al

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    Staff: Mentor

    The horizontal component of the tension provides the centripetal force.

    Analyze both vertical and horizontal components of the forces on the "man + swing".
  8. Oct 29, 2006 #7
    Thank you Doc Al when you said the forces on the man and and the swing it hit me :)
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