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Homework Help: Centripetal force and total force?

  1. Aug 5, 2010 #1
    1. The problem statement, all variables and given/known data
    A 25 kg child is on a swing, which has a radius of 2.00 m. If the child is moving 4.0 m/s at the bottom of one swing, what is the centripetal force exerted by the ropes of the swing on the child? What is the total force exerted by the ropes when the swing is at its lowest point?

    2. Relevant equations
    a = v^2/r

    F = mv^2/r

    3. The attempt at a solution

    I have no problem with the first part of the question. You just use F = mv^2/r to figure out the centripetal force. However, I am not sure how to get the "total force." I know which way the tension is directed and everything. I'm just not really sure what total force is referring to. Any help would be greatly appreciated.

  2. jcsd
  3. Aug 5, 2010 #2


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    Draw the free body diagram. What is causing the centripetal force?

    Everything is easier because the problem asks you about the lowest point, so forces either point up or down.
  4. Aug 5, 2010 #3


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    Homework Helper

    The word "total" isn't necessary in that question. You can just as well think of it as "What is the force exerted by the ropes when the swing is at its lowest point?"
  5. Aug 5, 2010 #4


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    edit: nvm
  6. Aug 5, 2010 #5
    So what it is asking for is basically the tension in the rope? If so, that is easy.

    Fc = Ft - Fg

    Solve for Ft.

    The word "total" was throwing me off. I was convinced it meant Net force or something.
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