What is the Angular Velocity of a Pivoting Rod with a Rigidly Attached Weight?

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The discussion focuses on calculating the angular velocity of a pivoting rod with a weight attached, released from a 37° angle. The system consists of a 4 m rod and a 5.15 kg weight, with an angular acceleration of 2.17 rad/s². Energy conservation principles are applied, stating that the change in potential energy of both the rod and the weight equals the kinetic energy. It is clarified that the potential energy of the rod does not change since it pivots at its center of mass. The conversation highlights the importance of accurately calculating the potential energy changes to determine the angular velocity when the rod is vertical.
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https://tychosrv-s.phys.washington.edu/cgi/courses/shell/common/showme.pl?courses/phys121/spring05/homework/08/pivoting_rod_RSD/1.gif

A uniform rod is pivoted at its center and a small weight of mass M = 5.15 kg is rigidly attached to one end. The rod has length L = 4 m and mass mrod = 12.4 kg. The system is released from rest at the q = 37° angle. The angular acceleration just after it is released is 2.17rad/s^2. What is the angular velocity when the rod is vertical?

To do this, you can use the energy conservation. Change in potential energy of the rod plus the change in potential energy of the weight equals the kinetic energy. KE = (1/2)IW^2 = delta total Potentional energy. You get the change in potential energy by finding the delta PE of weight and the rod. delta PE of weight is simply M*G*(change in Height), but how do you find the change in PE of the rod?
 
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jhson114 said:
https://tychosrv-s.phys.washington.edu/cgi/courses/shell/common/showme.pl?courses/phys121/spring05/homework/08/pivoting_rod_RSD/1.gif

A uniform rod is pivoted at its center and a small weight of mass M = 5.15 kg is rigidly attached to one end. The rod has length L = 4 m and mass mrod = 12.4 kg. The system is released from rest at the q = 37° angle. The angular acceleration just after it is released is 2.17rad/s^2. What is the angular velocity when the rod is vertical?

To do this, you can use the energy conservation. Change in potential energy of the rod plus the change in potential energy of the weight equals the kinetic energy. KE = (1/2)IW^2 = delta total Potentional energy. You get the change in potential energy by finding the delta PE of weight and the rod. delta PE of weight is simply M*G*(change in Height), but how do you find the change in PE of the rod?

The potential energy of the rod does not change because the pivot point is the center of mass.
 
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thats what i thought too. i wasnt getting the right answer, but i guess i did the calculations wrong. thanks !
 
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