1. Not finding help here? Sign up for a free 30min 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!

Angular Speed, Glob and Rod

  1. Dec 20, 2006 #1
    1. The problem statement, all variables and given/known data
    [​IMG]

    On a frictionless table, a glob of clay of mass 0.38 kg strikes a bar of mass 0.90 kg perpendicularly at a point 0.55 m from the center of the bar and sticks to it. If the bar is 1.30 m long and the clay is moving at 8.1 m/s before striking the bar, at what angular speed does the bar/clay system rotate about its center of mass after the impact?

    2. Relevant Equations

    [tex]L_i=RXP=I\omega[/tex]

    [tex]cm_[new]=\frac{all m*d}{total mass}[/tex]

    Parallel Axis Theorem

    3. The attempt at a solution

    M is mass of rod and m is mass of glob.

    [tex]L_i=RXP=mvb=1.6929[/tex]

    [tex]L_f=I_{glob}\omega+I_{rod}\omega[/tex]

    [tex]\delta=distance from old cm to new cm[/tex]

    [tex]\delta=\frac{mb}{m+M}=.1633 m[/tex]

    [tex]I_{glob}=m(b-\delta)^2[/tex]

    [tex]I_{rod}=\frac{M(L)^2}{12}+M\delta^2[/tex]

    [tex]L_i=L_f[/tex]

    I get 8.15 rad/s which is wrong, the right answer is 5.743. What did I do wrong?
     
    Last edited: Dec 21, 2006
  2. jcsd
  3. Dec 21, 2006 #2

    Doc Al

    User Avatar

    Staff: Mentor

    This is the angular momentum of the blob about the center of the bar. What you need is the angular momentum about the center of mass of the system--that is the quantity that is conserved.
     
  4. Dec 21, 2006 #3
    So I should have [tex]L_i=mv(b-\delta)[/tex] ?

    Thanks, I got it.
     
    Last edited: Dec 21, 2006
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Angular Speed, Glob and Rod
Loading...