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Homework Help: Spinning Ball

  1. Jul 4, 2005 #1
    A mass M of 2.47 kg is attached to the end of a string whose length is 0.410 m. The mass slides without friction on a horizontal surface as indicated in the diagram.

    a)If the string can withstand a maximum tension of 113.1 N, what is the maximum tangential speed the ball can have before the cord breaks?
    Answ: 4.33 m/s

    b)The mass, with a new string, is whirled in a vertical circle of the same radius about a fixed point. Find the magnitude of the tension when the mass is at the top if its speed at the top is 6.69 m/s.
    Answ: 2.45×102 N

    For part a) i used the formulaa 1) F=ma 2)a=rw^2 3) V=rw to get the right answer but for part b) I used 1)V=rw 2) a=rw^2 3)T=ma but im not getting the right answer. Am I doing something wrong?
  2. jcsd
  3. Jul 4, 2005 #2
    Diagram please.

  4. Jul 4, 2005 #3


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    Homework Helper

    b) the motion is vertical, so you must take gravity into account.
  5. Jul 4, 2005 #4


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    Gold Member

    In the second case, gravity is also acting.
    So, mv^2/r=mg+T.
  6. Jul 4, 2005 #5
    T = m ((v^2/r)-g)
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