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: Angularr speed of disk

  1. Jun 1, 2010 #1
    A large flat disk with moment of inertia I is spinning with angular speed 18 rad/s
    a small object lands on the disk and changes the moment of inertia to 1.5I

    what is the new speed?

    i used L=I[tex]\omega[/tex] to give me 18*1.5=27 rad/s

    i used this because L is the angular momentum of the disk and has a relationship with the angular speed.

    Is this correct?
  2. jcsd
  3. Jun 1, 2010 #2
    Do you have an equation showing the conservation of angular momentum ie the angular momentum before and after the object lands on the disk? If the moment of Inertia of the item with angular momentum increases, should the angular speed also increase? dont think so...
    Last edited: Jun 1, 2010
  4. Jun 19, 2010 #3
    Re: angular speed of disk

    I think answer is incorrect.
    By the law of conservation of momentum,
    disk initial momentum+object initial momentum =(disk+object) final momentum
    object initial momentum is zero.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook