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Homework Help: Finding the speed of a trebuchet

  1. Mar 3, 2010 #1
    1. The problem statement, all variables and given/known data
    A simple trebuchet is shown in the figure. Model it as a stiff rod of negligible mass, 2.70 m long, joining particles of mass 73.0 kg and 0.100 kg at its ends. It can turn on a frictionless, horizontal axle perpendicular to the rod and 12.0 cm from the large-mass particle. The rod is released from rest in a horizontal orientation.

    The trebuchet is something like a seesaw with the pivot (in this case) being closer to the heavier weight.

    2. Relevant equations



    3. The attempt at a solution
    I tried to find the torque, T = 9.8(73*0.12 - 0.1*(2.7-0.12)) = 83.3Nm
    I find the Work, W = integrate T wrt to theta with limits from 0 to pi/2 = 131J
    v = sqrt(2*131/0.1) = 51.2m/s


    I also tried finding the moment of inertia, I = 67.6kgm2
    131 = 0.5 * 67.6 * w2
    v = r* w = 5.08m/s


    My concept for this topic on rotation of rigid object is very weak, so I hope someone can help me out with this question. Thanks
     
  2. jcsd
  3. Mar 3, 2010 #2

    Delphi51

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    Homework Helper

    No information has been given on how the rod is driven. Its final speed will depend on the torque applied to it during its swing.
     
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