1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook