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Homework Help: Rotating object: Finding Tension and Vtheta

  1. Apr 21, 2008 #1
    1. The problem statement, all variables and given/known data
    A string with 2kg mass m on the end is connected to a bar that rotates at a constant rate (theta dot). The string makes a constant angle beta, = 60 degrees relative to the horizontal plane. Find theta dot and the tension force in the string.

    2. Relevant equations

    3. The attempt at a solution

    I realize this may be very difficult to understand without a picture, but the rotation is in the x y direction I suppose and gravity is acting downward in the Z direction. I'm not really sure how to go about this problem. There's a specific velocity that will give the angle relative to the x axis the 60 degrees but I'm quite stuck, any help would be great.
  2. jcsd
  3. Apr 21, 2008 #2
    Maybe this is right?

    Ok so after fighting through it again, I realized what might work...

    F(z) = 0; Tcos(30) - 2kg*9.81 = 0: T = 22 N

    F(n) = ma(n); 22sin(30) = 2(v^2/1.57)

    I realized I also forgot to mention the p value: 1.57
  4. Apr 21, 2008 #3


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    Looks good so far. The solution of the 2nd equation will give you 'v'. After determining what 'v' represents, you must now determine theta dot.
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