Results 1 to 4 of 4
Like Tree1Thanks
  • 1 Post By hollywood

Math Help - Very basic moment of inertia question

  1. #1
    Member
    Joined
    Sep 2011
    Posts
    75

    Very basic moment of inertia question

    26-5-7

    Find the moment of inertia of a plate covering the region bounded by x = -1, x = 1, y = 0 and y= 1 with respect to x axis.

    Basic equation
    Ix = k integral (x^2 * y)
    x^2 * 1
    = x^2
    Integrate x^2:
    1/3x^3

    so the answer is k * 1/3x^3
    and we would plug 1 into x?

    the book answer is 2/3k... any hints? thanks.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    Joined
    Mar 2010
    Posts
    980
    Thanks
    236

    Re: Very basic moment of inertia question

    I think you have an extra y in the basic equation - it should be I_x=k\int\int x^2\,dx\,dy =k\int_{-1}^1x^2\,dx =\frac{2}{3}k.

    - Hollywood
    Thanks from topsquark
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Sep 2011
    Posts
    75

    Re: Very basic moment of inertia question

    sorry still not understanding how you got 2/3k in the end
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Super Member
    Joined
    Mar 2010
    Posts
    980
    Thanks
    236

    Re: Very basic moment of inertia question

    Here's how I did the last step:

    k\int_{-1}^1x^2\,dx =k\left[\frac{x^3}{3} \right]_{-1}^1 =

    k\left( \frac{(1)^3}{3}-\frac{(-1)^3}{3} \right) = k\left( \frac{1}{3} - \frac{-1}{3} \right)= \frac{2}{3}k.

    - Hollywood
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Moment of Inertia
    Posted in the Calculus Forum
    Replies: 18
    Last Post: December 19th 2011, 11:00 AM
  2. [SOLVED] Moment of Inertia
    Posted in the Calculus Forum
    Replies: 1
    Last Post: September 4th 2011, 10:01 PM
  3. Moment of Inertia
    Posted in the Calculus Forum
    Replies: 1
    Last Post: July 5th 2010, 11:59 AM
  4. Moment of inertia
    Posted in the Calculus Forum
    Replies: 3
    Last Post: March 30th 2009, 12:06 PM
  5. Second moment of inertia.
    Posted in the Advanced Math Topics Forum
    Replies: 2
    Last Post: April 24th 2006, 08:23 AM

Search Tags


/mathhelpforum @mathhelpforum