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Homework Help: Dynamics question!

  1. Jan 19, 2012 #1
    Ok, i'm doing Mechanical Engineering so my assumption was to post in here?

    I'm doing a dynamics module and revising for an up and coming exam. One of the 'revision' questions doesn't have the answer to work through, and typically im finding it very difficult to get my head around it.

    The question:

    The two uniform thin discs shown in the figure below rest on a horizontal plane
    and are connected through frictionless pin-joints at A and B by a rigid rod AB of
    negligible mass which remains horizontal. The mass of disc A is 15 kg and that of
    disc B is 25 kg. The static coefficients of friction between the plane and disc A and
    B are 0.2 and 0.55, respectively, and the dynamic coefficients of friction are 0.15
    and 0.45, respectively. At the instant shown, a counter-clockwise moment
    T = 125 Nm. is applied to disc B. You are required to
    (a) identify the type of ensuing motion of the discs,
    (b) draw the free-body, kinematic and kinetic diagrams of the discs,
    (c) write down the appropriate kinetic and kinematic relationships with
    respect to a global reference axes system, indicating any assumption
    made and
    (d) determine the magnitudes and senses of the angular accelerations of
    the discs and force developed, if any, in the rod AB.
    (e) If slipping is anticipated, indicate with supporting arguments, whether
    one of the discs will first slip or both will slip at the same time.
    You must clearly show details of the analysis you have carried out using
    equations in part (c) above to arrive at the results in part (d) in a reasonably
    logical way.


    a) Im assuming its Rotational? But it moves position, so maybe circular motion?

    b) Do i break down each component and do the FBD etc on each bit? Or do it as one big chunk? This is as far as i am....
  2. jcsd
  3. Jan 26, 2012 #2
    looking at notes i have from uni i would say that its either curvinlinear motion or general plane motion
  4. Jan 26, 2012 #3
    oo i didn't expect a reply so i haven't been checking this!

    Yes, i've made some progress and i agree, i think its General Plane Motion. I've made my FBD, Kinetic and Kinematic diagrams. ill upload them later and see if anyone can point me in the right direction!

  5. Jan 27, 2012 #4
    Is there a reaction force on both discs in the Y direction where the bar connects to the disc? Or is it just in the x direction?
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