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Registered Member #617
Joined: Fri Mar 30 2007, 07:29PM
Location: Buffalo NY
Posts: 49
The attached image is some homework due tomorrow and no one in my class (all three of us) knows how to solve it. I know this forum isnt for things like this but i thought that some of you might like to have some fun with physics and help a kid out. thanks even if you dont answer, but if you did, i might destroy my next mosfet in your name :)
the equation for angular momentum is L=rxp where p is the linear momentum (.12Ns) and r is the position of the particle expressed as a displacement vector from the origin, the center of mass of the system is 4cm from the center of the larger puck along the axis. so in that case, from which particle do i use as my reference point to find the angular momentum relative to the center of mass? i know why only three of us take the class.
[Edit: Double posting is forbidden under Part II subsection G of the rules, so a moderator kindly merged the two posts]
Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
It doesn't say the puck are moving in any direction after they touch so you can assume that all the energy of the first puck goes into spinning the pair of them. You should be able to take that value and work backwards with your angular momentum equations to find the speed of the spin.
Registered Member #8
Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214
Haha, a blue problem. Does that mean it's from Serway/Jewett? Anyway yeah, you just have to find the moment of inertia for the two pucks together, and transfer the linear momentum to that as angular momentum.
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