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!

Finding a common angular velocity

  1. Nov 15, 2008 #1
    1. The problem statement, all variables and given/known data
    A disk is rotating freely at 1,000 revolutions per minute about a vertical axis through its center. A hoop with twice the mass of the disk and the same radius as the uniform disk is poised exactly above and is initially at rest. The hop is dropped gently upon the disk so that their rims coincide. The common angular velocity of the disk-hoop combination is:


    2. Relevant equations
    Conservation of Angular Momentum:
    I1w1 = I2w2


    3. The attempt at a solution
    I1w1 = I2w2
    1/2MR^2 x 1000 rpm = 2MR^2 w2

    w2 = 1/2MR^2 x 1000 rpm/ 2MR^2
    w2 = 250 rev/min

    is this correct?
     
  2. jcsd
  3. Nov 15, 2008 #2

    alphysicist

    User Avatar
    Homework Helper

    Hi lmc489,

    I don't believe this is correct. On the right hand side you only have the angular momentum of the hoop. You need the total angular momentum of the entire hoop-disk system.
     
  4. Nov 15, 2008 #3
    oh YES! i forgot. so instead the answer would be 200 right?
     
  5. Nov 15, 2008 #4

    alphysicist

    User Avatar
    Homework Helper


    That looks right to me (if you want the answer in rpm).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Finding a common angular velocity
Loading...