1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Angular momentum

  1. Jan 28, 2017 #1
    1. The problem statement, all variables and given/known data
    There is a man walking on a disk with mass 70 kg and speed 4 m/s. He walks on a circle with radius 1,5 m. How fast does the disk (mass 200 kg and radius 2 m) under him rotates (need to calculate angular velocity)


    2. Relevant equations
    angular momentum = J * w (J-moment of inertia, w, angular velocity)

    3. The attempt at a solution
    (J_disk) * (w_disk) = (J_man) * (w_man)
    1/2 MR^2 *(w_disk) = (mr^2* ( v_man)) / r
    (w_disk) = mr(v_man) / MR^2
    (w_disk) =1,05 /s

    What am I doing wrong?
  2. jcsd
  3. Jan 28, 2017 #2
    I have already solved it. It is so so easy (I knew that before, that is why I was asking here, as I was sure that my answer was correct). I did not see that it was written that the velocity (4m/s) meant the velocity of a man towards the disk, not towards the observer somewhere out of the disk.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted