Rotation - Angular Momentum

  • #1
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Homework Statement


attachment.php?attachmentid=33194&stc=1&d=1300392775.jpg



The Attempt at a Solution



I did it like this:

[tex]\vec{L}_{B \ wrt \ Ground} = \vec{L}_{B \ wrt \ A} + \vec{L}_{A \ wrt \ Ground}[/tex]

[tex]\vec{L}_{B \ wrt \ A} = \vec{L}_{B \ wrt \ Ground} - \vec{L}_{A \ wrt \ Ground}[/tex]

so

[tex]\vec{L}_{B \ wrt \ A} = mwd^2 \ - \ \frac{1}{4}mwd^2[/tex]

[tex]\vec{L}_{B \ wrt \ A} = \frac{3}{4}mwd^2[/tex]

why is my method wrong?
 

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Answers and Replies

  • #2
tiny-tim
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hi cupid.callin! :smile:
[tex]\vec{L}_{B \ wrt \ A} = \vec{L}_{B \ wrt \ Ground} - \vec{L}_{A \ wrt \ Ground}[/tex]
sorry, but this doesn't work at all :redface:

LA(B) = rAB x (vB - vA)

= (rOB - rOA) x ((vB - v0) - (vA - vA)) …

bits of that are the RHS of your equation, but that's all
 
  • #3
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Why is does not work,:cry:

Is it because the eqn i used relates velocity or acceleration of particle wrt to a non inertial particle or frame ??? :confused:
 
  • #4
tiny-tim
Science Advisor
Homework Helper
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why should it work? :confused:

it obviously doesn't work …

the RHS of your equation is rOB x vB - rOA x vA
 

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