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!

F=ma 2011 number 24

  1. Jan 26, 2014 #1
    1. The problem statement, all variables and given/known data

    A turntable is supported on a Teflon ring of inner radius R and outer radius R+δ (δ  R), as shown in the diagram.
    To rotate the turntable at a constant rate, power must be supplied to overcome friction. The manufacturer of the
    turntable wishes to reduce the power required without changing the rotation rate, the weight of the turntable, or
    the coefficient of friction of the Teflon surface. Engineers propose two solutions: increasing the width of the bearing
    (increasing δ), or increasing the radius (increasing R). What are the effects of these proposed changes?


    (A) Increasing δ has no significant effect on the required power; increasing R increases the required power.
    (B) Increasing δ has no significant effect on the required power; increasing R decreases the required power.
    (C) Increasing δ increases the required power; increasing R has no significant effect on the required power.
    (D) Increasing δ decreases the required power; increasing R has no significant effect on the required power.
    (E) Neither change has a significant effect on the required power.

    http://www.aapt.org/physicsteam/2012/upload/exam1-2011-1-3-answers_1.pdf (number 24)

    2. Relevant equations
    P=Fv=Tw


    3. The attempt at a solution
    I have no idea how to start this.... Also I don't understand the situation. Is the turntable like a box on top of the ring? Or do they mean they have a vinyl disc on top of the ring? I have no idea what they're talking about.
     
  2. jcsd
  3. Jan 26, 2014 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    What difference does it make if the turntable is a vinyl disk or some sort of box?
    What matters is how the friction with the teflon ring depends on the dimensions of the ring.

    Anyway - the diagram should give you a hint.
     
  4. Jan 26, 2014 #3
    I have no idea where the friction force would be located... Would it be concentrated at the middle of the ring width?
     
  5. Jan 26, 2014 #4

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

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: F=ma 2011 number 24
  1. 2011 F=ma #13 (Replies: 1)

  2. 2009 f=ma #24 (Replies: 1)

Loading...