1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Angular speed question please help right away!

  1. Dec 14, 2004 #1
    angular speed question!! please help right away!

    a pencil, 15.7 cm long, is released from a vertical position with the eraser end resting on a table. The eraser does not slip. Treat the pencil like a uniform rod. what is the angular speed of the pencil just before it hits the table?

    i know i have to use conservation of energy, but im not sure where center of mass fits in.. please help

    the answer choices are:
    a. 11.2 rad/s
    b. 7.23 rad/s
    c. 24.5 rad/s
    d. 16.8 rad/s

    any help or guidance would be much appreciated..thank u!
  2. jcsd
  3. Dec 14, 2004 #2

    Doc Al

    User Avatar

    Staff: Mentor

    In figuring the change of PE of the pencil, use the change in height of the center of mass. The PE gets converted to rotational KE.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook