# Moment of Inertia + Energy question

1. Nov 3, 2007

### darkspym7

1. The problem statement, all variables and given/known data
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?

2. Relevant equations
U=mgh
K=1/2Iw^2

3. 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=$$\sqrt{\frac{6gh}{L^2}}}$$, 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?

2. Nov 4, 2007

### darkspym7

Here's the figure that went along with it:

http://img103.imageshack.us/img103/9987/hw10q1ex1.jpg [Broken]

Last edited by a moderator: May 3, 2017
3. Nov 4, 2007

Anyone?

4. Nov 4, 2007

### darkspym7

I still don't know.