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Freefall angular momentum

  1. Oct 9, 2009 #1
    1. The problem statement, all variables and given/known data
    a mass drops from rest without air resistance, starting from coordinates x=xo, y=yo, z=0. compute its angular momentum about origin at time=t. compare it to the torque on the mass. repeat this, but pick your origin for the angular momentum and torque about the point (x,y,z)=(2xo, 0,0).

    2. Relevant equations

    3. The attempt at a solution
    gravity is the only force so mg=dp/dt. separating and integrating, mgt=p. this is way too simple, how should i attack this problem? i feel that i am not given enough information
  2. jcsd
  3. Oct 9, 2009 #2
    [tex]\vec L= \vec R\times \vec P[/tex]

    [tex]\frac{d\vec L}{dt}=\Sigma \vec \tau[/tex]

    These should straighten things out for you. You found the linear momentum of the object, now find the angular momentum.
    Last edited: Oct 9, 2009
  4. Oct 10, 2009 #3
    but how? what is r and what is p with the info i am given?
  5. Oct 10, 2009 #4
    [tex]\vec R[/tex] is the distance between the object and the point about which you're measuring the angular momentum and torques.

    [tex]\vec P[/tex] is the linear momentum of the mass.

    [tex]\Sigma \vec \tau[/tex] is the net torque on the mass.

    What I posted was the definition of angular momentum, I am surprised you aren't familiar with it.

    The second formula relates torque with angular momentum.
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