- #1
Mikkel
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Homework Statement
Hello!
I apologize for my poor setup, first post.
I am given a system of two rods, hope you can see my image.http://file:///C:/Users/Mikkel/Downloads/Mek2_exam_Jan2016_final.pdf
One along the x-axis with mass = 2m and length = 2l
Another perpendicular with the other with mass = m and length = l
The system rotate around a point O
Find the angular velocity at the point when the systems longest rod is vertical.
Homework Equations
I have calculated the center of mass rcm = ( (4/3)*l , (1/6)*l )
and the distance from pivot point to the center of mass = (1/6) * sqrt(65) * l
Also the moment of inertia for the system = 7*m*l2
The Attempt at a Solution
I have tried the following so far:
I tried to use conservation of energy to solve it:
m*g*h + 0 = 0 + (1/2)*I*w2
I am thinking that I have a total of mass 3
and the height has to be the x-coordinate for center of mass (I think this is where I might be wrong?)
3*m*g*(4/3)*l = (1/2)*7*m*l2 * ω2
after a bit of calculations...
ω = sqrt((8*g)/(7*l))
However my facit says ω = sqrt((9*g)/(7*l))
I can't figure it out!
Appreciate any tips ! :)
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