Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook