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Homework Help: String and ball

  1. May 1, 2010 #1
    1. The problem statement, all variables and given/known data
    If a ball is attached to a string and is swung in the air, does the string do the work on the ball?


    2. Relevant equations

    none

    3. The attempt at a solution

    I have tried to figure it out. I have thought that it did because the string was the force that made the ball swing but then I thought it was the hand holding the string that was doing the work. I am very confused about this and have been unable to find anything about it in my book.
     
  2. jcsd
  3. May 1, 2010 #2

    PhanthomJay

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    What is the definition of the work done by a force?
     
  4. May 1, 2010 #3
    I am not sure what your reply means. Was it a question? Forgive me but I am out of my element in this class. I have no prior math other then algebra and formulas get me lost. I was not sure about the work done. The problem is a picture of a hand holding a string with a ball on it and is swinging it so the ball is moving in a circular motion. The statement is 'The string is doing work on the ball' We are to say if this is a true or false statement. I was not sure what force of energy it is and whether or not it was true. I looked in my book and my lecture notes but found no answers. If you can help I would greatly appreciate it.
     
  5. May 2, 2010 #4

    PhanthomJay

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    Hi, teres

    Homework help is provided on these forums. We try to guide you in the right direction so that you yourself can come up with the answer. We do not directly provide the answers.

    The string does exert a force on the ball. In order to determine whether or not that force is doing work on the ball, you must go back to the basic definition of work. Is there a formula in your lecture notes that looks something like W = F(d)cos theta?? The key here is to determine the value of theta, which is the angle betweeen the force and the direction of the ball's displacement.
     
  6. May 2, 2010 #5
    I have never seen this formula before. There has not been anything about the value of theta in our book. I wasn't asking for the answer, just some help in understanding it.
     
  7. May 2, 2010 #6

    PhanthomJay

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    A force does work if there is a displacement of that force in the direction of its application. Does the string move in the direction of its tension force?
     
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