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Trouble be force diagram, verticle circle

  1. Dec 4, 2009 #1
    Hello all,

    I seem to be having issues drawing the correct force diagrams... The question is as follows:

    "A 1kg mass, attached to the end of a string, is swung in a vertical circle having radius of 0.3m. When the string makes and angle of 30 degrees below horizontal, the speed of the mass is 3.0m/s.

    My attempt at the solution (I know the force diagram is where I'm going wrong) is in the picture along with my drawn diagram. (It's attached to this thread)

    Note: phi is simply 90-30 = 60 degrees. I also forgot to put a dash inbetween mg and sin(theta)

    It should look like this:

    T - mg/sin(theta) = ma
    T = m[(v^2)/r] + mg/sin(theta)
     

    Attached Files:

  2. jcsd
  3. Dec 4, 2009 #2

    nrqed

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    Hi there

    It is the triangle you drew with mg and h that is incorrect. You drew it with h being the hypothenuse.

    But it is the force mg which should be the hypothenuse of your right angle triangle. h should be a shorter side (one of the shorter sides will be tangent to the circle and the other short side will be parallel with the radius)

    By the way, what software did you use for your drawing? I am just curious.
     
  4. Dec 4, 2009 #3
    Thank you! I knew my mistake wasn't in the mg triangle I just couldn't see how to repair it!

    I used an online whiteboard to make my drawings. (www.scriblink.com[/URL])
     
    Last edited by a moderator: Apr 24, 2017
  5. Dec 4, 2009 #4

    nrqed

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    Last edited by a moderator: Apr 24, 2017
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