1. Not finding help here? Sign up for a free 30min 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!

Angular Velocity of a turntable-man system

  1. Dec 16, 2008 #1
    1. The problem statement, all variables and given/known data
    A turntable rotates about a fixed vertical axis, making one revolution in 10s. The moment of inertia of the turntable about the axis is 1600kgm^2. A man, James Bond, of mass 120kg, is at the center of the turntable and begins to run out along a radius of the device. Treat the man as a point object.


    2. Relevant equations
    L = Iw


    3. The attempt at a solution
    There are three parts. The first part asks for the initial angular velocity, which is simply converting 1rev/10s into rad/s. The second part asks for the initial angular momentum, which would be L = Iw?

    The third part is asking for the angular velocity of the turntable-man system when the man is 2m from the center of the turntable. It also says at this point the man is at rest with respect to the turntable.

    Now I run into my problems. I'm not too sure about how to calculate this, but one method I'm thinking of is recalculating the inertia to be 1600kgm^2 + mr^2 where m and r are referring to the man (so 120kg and 2m respectively). This would give an inertia of 1840kgm^2.

    I thought about using L = r (cross) p, but solving for the linear momentum would mean finding Vtan = wr? How would I find w in this case?
     
  2. jcsd
  3. Dec 16, 2008 #2

    rl.bhat

    User Avatar
    Homework Helper

    Since there is no external torque acting on the tern table, angular momentum remains constant.
     
  4. Dec 16, 2008 #3
    I was considering that approach but wasn't sure. Thanks. However, my approach to the new inertia would be correct, I assume?
     
  5. Dec 16, 2008 #4

    rl.bhat

    User Avatar
    Homework Helper

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?