- #1
ENgez
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suppose i have a solid rod of length 2L, connecting two identical point masses on either side, and this system is spining around the center of mass at a steady angular speed of [tex]\omega[/tex]. another identical point mass is placed so that it collides with one of the point masses when the rod is horizontal. let's say you want to find [tex]\omega[/tex] at the center of mass after the collision, using conservation of angular momentum.
this is where i am confused: I know the center of mass changes after the collision, and, assuming the origin is on the initial center of mass and the right and up directions are positive, calculated it to be: L/3.
Now, the way i understood this in class, To answer this question i must compare the angular momentum right before and after the collision.
but i recall that you can't directly compare the angular momentum at the axis that goes throught the initial center of mass and the angular momentum at the axis of the new center of mass after the collision, so i figured out the angular momentum at the axis of the new center of mass before the collsion and then using:
[tex]I_{before}\omega=I_{after}\omega_{needed}[/tex]
found out [tex]\omega_{needed}[/tex].
The porblem is that the lecture notes compare the axis of the initial center of mass before collision directly to the axis of the new center of mass after colision. Is this a mistake or am i missing something?
this is where i am confused: I know the center of mass changes after the collision, and, assuming the origin is on the initial center of mass and the right and up directions are positive, calculated it to be: L/3.
Now, the way i understood this in class, To answer this question i must compare the angular momentum right before and after the collision.
but i recall that you can't directly compare the angular momentum at the axis that goes throught the initial center of mass and the angular momentum at the axis of the new center of mass after the collision, so i figured out the angular momentum at the axis of the new center of mass before the collsion and then using:
[tex]I_{before}\omega=I_{after}\omega_{needed}[/tex]
found out [tex]\omega_{needed}[/tex].
The porblem is that the lecture notes compare the axis of the initial center of mass before collision directly to the axis of the new center of mass after colision. Is this a mistake or am i missing something?