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!

Dynamics Homework Problem

  1. Jan 31, 2010 #1
    1. The problem statement, all variables and given/known data
    A 3-lb collar can slide on a horizontal rod which is free to rotate about a vertical shaft. The collar is intially held at A by a cord attached to the shaft. A spring constant of 2 lb/ft is attached to the collar and to the shaft and is undeformed when the collar is at A. As the rod rotates at the rate ThetaDot=16 rad/s, the cord is cut and the collar moves out along the rod. Neglecting friction and mass of the rod, determine

    a)the radial and transverse components of the acceleration at A

    b)The acceleration of the collar relative to the rod at A

    c)the transverse component of the velocity of the collar at B


    2. Relevant equations



    3. The attempt at a solution
    I know the solution to the problem. The answers are
    a) Ar=0, Atheta=0

    b)1536 in./s^2

    c)32.0 in/s

    I don't feel like this is a difficult problem, but I am definitely missing a key concept. How can you determine these quantities without r as a function of time?
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

    • 1290.png
      1290.png
      File size:
      33.6 KB
      Views:
      176
  2. jcsd
  3. Feb 1, 2010 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Hi negatifzeo! :smile:

    (have a theta: θ and an omega: ω and try using the X2 tag just above the Reply box :wink:)
    I suppose you're wondering how you can find r'' without knowing r(t)? :redface:

    It doesn't matter, because you can work it out from good ol' Newton's second law … Fradial = m(r'' - ω2r) :wink:
     
  4. Feb 1, 2010 #3
    The angular velocity is given. The mass is given. But we don't know the total force, do we? The total force is broken up into two components, "e-sub-r" and "e-sub-theta", which we do not know.
     
  5. Feb 1, 2010 #4

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Hi negatifzeo! :smile:

    (what hapened to that θ i gave you? :redface:)
    You won't need the eθ component of the force.

    Try it for a) first. :smile:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Dynamics Homework Problem
  1. Dynamics Problem (Replies: 1)

  2. Dynamics Homework Help (Replies: 3)

Loading...