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: Rotating pendelum

  1. Apr 27, 2010 #1
    1. The problem statement, all variables and given/known data

    A uniform stick of length L = 2.2 m, width W = 9.0 cm, and mass M = 4.5 kg oscillates as a physical pendulum and pivots about point O as shown in the Figure. What is the period of the pendulum if x, the distance from the pivot point to the center of gravity of the pendulum, is equal to 0.68 m?

    2. Relevant equations

    T=2*pi*sqrt(L/g)

    3. The attempt at a solution

    I am stuck, i know 2*pi*sqrt((1.1+.68)/9.81) is not going to be right because the section of the stick above the pivot needs to be taken into account, im just not sure how.
     
  2. jcsd
  3. Apr 28, 2010 #2

    ehild

    User Avatar
    Homework Helper

    It is a physical pendulum. The formula for T you cited is not valid for it.

    Determine I, the moment of inertia with respet to the pivot point. Find the distance d between the centre of mas and the pivot.

    T = 2 pi sqrt[I/(mgd)]

    ehild
     
  4. Apr 28, 2010 #3
    ah ok, how does width factor into the inertia? i was going to do
    (4.5*(1.1+.68)^2/(2.2*3))+(4.5*(2.2-1.10.68)^2/(2.2*3)) but 1/3mL^2 is for a stick that is infinitly thin, not sure how to compensate for width.
     
  5. Apr 28, 2010 #4

    ehild

    User Avatar
    Homework Helper

    It is not infinitely thin. Find a formula somewhere which fits to the picture of this pendulum. (You did not show it)

    ehild
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook