Finding the speed of a trebuchet

  • #1

Homework Statement

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.

Homework Equations

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
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  • #2
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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