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!

What's wrong with my answer?

  1. Feb 17, 2015 #1
    1. The problem statement, all variables and given/known dataThe question says
    A chain of mass per unit length k and length 1.5 m rest on a fixed smooth sphere of radius R= 2/π m
    . Tension in the thread is asked.The question figure is attached.


    2. Relevant equations
    N/a


    3. The attempt at a solution
    IMG_20150217_145935.jpg IMG_20150217_145935.jpg
    I think that the tension has to balance two types of forces :
    1) rightward force of part AC(touching)
    2)downward force of part CB(hanging)
    Finding first type of force:
    Using Fbd(attached) of small part taken in touching part
    Then Ncos(theta)=(dm)g
    → N=(dm)g/cos(th.).......(1)
    Length of that part =R(d(th.))
    mass of that small part =Rk(d(th.))
    Using Fbd rightward force on the small part =Nsin(th.)=(dm)g(tan(th.))
    =Rkgtan(th.)(d(th.))
    Now if I want to integrate it , i would have to use limits from 0 to π/2
    BUT tan (th.) is not integrable b/w 0 to π/2 . So whats wrong with my answer ?
     

    Attached Files:

  2. jcsd
  3. Feb 17, 2015 #2

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I'm missing something in your force balance for the little chunk of chain. I see an N and an mg and they clearly don't balance. What force could possibly complete the picture ?
     
  4. Feb 20, 2015 #3
    It could have been friction BUT the sphere is smooth so , what can be the force (you are talking about ) left out that balances the tension of the thread ?
     
  5. Feb 21, 2015 #4

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    But you don't have the tension in the chain in the equation. Indeed, that's what's missing. Remember, it will not be constant along the the chain.
     
  6. Feb 21, 2015 #5
    You have to consider the tension on both sides of the element along the tangential direction!
     
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: What's wrong with my answer?
Loading...