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!

Help with a statics/dynamics question?

  1. Mar 17, 2015 #1
    Hi all,

    I often find myself on this forum when searching google for help on certain topcis, but I only just joined :)

    I am having trouble with a homework question. The question states:

    If the rod starts from rest in the position shown and a motor drives it for a short time with an angular acceleration of Alpha = (1.5e^t ) rad/s2 , where t is in seconds, determine the magnitude of the angular velocity and the angular displacement of the rod when t = 3s. Locate the point on the rod which has the greatest velocity and acceleration, and compute the magnitudes of the velocity and acceleration of this point when t = 3s. The rod is defined by z = 0.25 sin(Pi y) m, where the argument for the sine is given in radians and y is in meters.

    I have attempted the first section, which I think is correct however it seems too simple/odd to me.

    Here is a link to the actual question (with diagram), and my working so far.

    http://i1374.photobucket.com/albums/ag430/Drvirz/Problem 1_zpsidqrzizz.jpg

    https://www.dropbox.com/s/7ibtkysyvxxag64/DSC_0124.JPG?dl=0

    If anyone could confirm this is correct/incorrect and provide an insight into the rest of the question that would be fantastic!

    Thanks in advance!

    Josh
     
  2. jcsd
  3. Mar 17, 2015 #2

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    You should have read the Rules of PF when your joined. There is a HW section which is displayed very prominently at the top of the PF website. I'm moving this thread to the Intro Physics HW forum.
     
  4. Mar 17, 2015 #3
    You appear to have integrated correctly to find the angular velocity function. But it says to solve it for when t=3. As for the next part try to find an equation for the angular displacement of the rod with respect to time.
     
  5. Mar 17, 2015 #4

    Delta²

    User Avatar
    Gold Member

    You forgot the constants of integration in ur equations, should be easy to that the first constant for the angular velocity is -3/2, you should also compute the second for the equation of theta.

    The point with the maximum velocity and acceleration is that with the maximum z. You should find the y for which z becomes maximum. Then the velocity is [itex]ωz_{max}[/itex] and the acceleration is [itex]Alphaz_{max}[/itex].
     
    Last edited: Mar 17, 2015
  6. Mar 17, 2015 #5
    Never mind you already did that. Then you should ask yourself which part of the rod has the greatest velocity. The equation v= ωr should help...
     
  7. Mar 17, 2015 #6
    Sorry SteamKing, I will take note for future, and also read the rules.

    Just noticed your second comment. I will try and work through the next section and see how i go
     
  8. Mar 17, 2015 #7
    Ok so more or less z=0.25sin(Pi*y) for 0<y<1

    So find Z(max) by subbing y-value between 0-1 that will give largest z?
     
  9. Mar 17, 2015 #8

    Delta²

    User Avatar
    Gold Member

    yes but dont forget the constants of integration, the equation for theta becomes a bit different due to the presence of constant of integration in the equation for ω.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Help with a statics/dynamics question?
Loading...