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Moment of Inertia + Energy question

  • Thread starter darkspym7
  • Start date
  • #1
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Homework Statement


A uniform rod of mass 3 kg is 17 m long. The rod is pivoted about a horizontal, frictionless pin at the end of a thin extension (of negligible mass) a distance 17 m from the center of mass of the rod. Initially the rod makes an angle of 66◦ with the horizontal. The rod is released from rest at an angle of 66◦ with the horizontal, as shown in the figure below The acceleration of gravity is 9.8 m/s2.
Hint: The moment of inertia of the rod about its center-of-mass is Icm = 1/12mL^2.

What is the angular speed of the rod at the instant the rod is in a horizontal position?
Answer in units of rad/s.


Homework Equations


U=mgh
K=1/2Iw^2


The Attempt at a Solution


The moment of inertia I got for the whole system was:
I=M(L/2)^2+1/12ML^2
I've managed to get:
w=[tex]\sqrt{\frac{6gh}{L^2}}}[/tex], with w being the angular speed
But I am unsure if h is L*sin(theta) or (3/2L)*sin(theta), since the rod is off the pivot.

Any ideas?
 

Answers and Replies

  • #2
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Here's the figure that went along with it:

http://img103.imageshack.us/img103/9987/hw10q1ex1.jpg [Broken]
 
Last edited by a moderator:
  • #3
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Anyone?
 
  • #4
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I still don't know.
 

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