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Homework Help: Tension and centripital force revisited

  1. Apr 30, 2008 #1
    A 2.0 kg ball is attached to a vertical post with two strings, one 2.0 m long and the other 1.0 m long as shown in the figure. If the ball is set whirling in a horizontal circle, what is the minimum speed necessary for the lower string to be taught? If the ball has a constant speed of 6 ms-1, find the tension on each string.


    |\
    | \
    | \ -2.0m
    | \
    | \
    |----0 -2.0kg
    |
    | ^1m


    For the first part, figured that the 2m string has two components of tension Tsin60 and Tcos60.
    Tsin60=mg=19.6
    Tcos60=mv^2/r=2v^2
    tan60=19.6/2v^2
    v=5.66 m/s

    is that right? I calculated the angle that the 2m string made w/ the x-axis and went from there...

    Now..for the second part..
    i figured that the tension in the 1m string is the centripital force which is:
    T=mv^2/r=2*36/1= 72N
    Now for the second string..what would the tension be?
    i'm guessing i have to use the Tsin60 and the Tcos60
    Tsin60=19.6N
    Tcos60=72N
    T=sqrt(19.6^2+72^2)
    T=74.6N

    I hope this is right, i did all the work, i'm just looking for confirmation please
     
  2. jcsd
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