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: Moment of inertia of an irregularly shaped object

  1. Feb 24, 2005 #1
    This problem describes one experimental method of determining the moment of inertia of an irregularly shaped objectt such as the payload for a satelite. http://home.earthlink.net/~suburban-xrisis/clip2.jpg [Broken] shows a mass m suspended by a cord wound around a spool of radius r, forming part of a turntable supporting the object. When the mass is released from rest, it descends through a distance h, acquiring a speed v. Show that the moment of inertia I of the equptment (including the turntable) is [tex]mr^2(2gh/v^2-1)[/tex].

    here's what I tried, by using this fromula I found in the book:






    I'm not sure how to get the right answer.
    Last edited by a moderator: May 1, 2017
  2. jcsd
  3. Feb 24, 2005 #2
    Divide each of the terms in the bracket by v^2.
  4. Feb 24, 2005 #3






    This does not equal

    what did I do wrong?
  5. Feb 24, 2005 #4

    [tex]I=mr^2 * \frac{2gh-v^2}{v^2}[/tex]

    [tex]\frac{2gh-v^2}{v^2} = \frac{2gh}{v^2} - 1[/tex]

    [tex]I=mr^2(\frac{2gh}{v^2} - 1)[/tex]
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook