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!

A few dynamics questions

  1. Mar 29, 2009 #1


    User Avatar
    Homework Helper

    1. The problem statement, all variables and given/known data

    http://img18.imageshack.us/img18/4180/82081641.jpg [Broken]
    http://img14.imageshack.us/img14/2650/26169677.jpg [Broken]

    http://img13.imageshack.us/img13/6657/diagramsx.jpg [Broken]

    2. Relevant equations

    3. The attempt at a solution

    For the first one, the solutions are different from mine, but here is what I did:

    Note [itex]\times[/itex] denotes the cross-product

    [tex]v_B=\vec{\omega_B} \times \vec{r_{CB}}[/tex]
    [tex]v_B=2.5k \times 0.045j=-0.1125j[/tex]

    [tex]v_A=\vec{\omega_A} \times \vec{r_{OA}}[/tex]
    [tex]v_A= 3k \times 0.06i=0.18j


    Now, [itex]\vec{r_{AB}}= 0.09i+0.12j[/itex]

    [tex]\vec{\omega_{AB}} \times \vec{r_{AB}}= w_{AB}k \times (0.09i+0.12j)[/tex]
    [tex]\Rightarrow \vec{v_{AB}}=-0.12 \omega_{AB}i+0.09\omega_{AB}j[/tex]

    and if I compare components I get two different values for [itex]\omega[/itex]

    For the second question, the first thing I'd do is get the moment of inertia of the rod about the centre using (1/12)mL^2 and then say Ia=Torque to get a, then use F=ar to get the force needed. But I do not know if I should assume the rod is uniform and use the parallel axis theorem.

    For the third one, I am not too sure how to start that one. All I know that I can get from reading the question is the moment of inertia about the axis using the radius of gyration.
    Last edited by a moderator: May 4, 2017
  2. jcsd
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted