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!

Determining smallest possible diameter of a cable

  1. Apr 11, 2013 #1
    1. The problem statement, all variables and given/known data

    You have a round steel cable with diameter d and a ultimate strenght of 400Mpa.
    There is a force of 8,2KN working along the cable.
    What is the smallest possible diameter the cable can have without breaking?

    2. Relevant equations
    δ= N/A
    Area of a circle: πr^2


    3. The attempt at a solution

    δ= N/A = N/πr^2

    Where N is the force working on the cable and δ is the ultimate strength of the cable.

    Not sure about the placement of δ here:

    r^2 = N/δπ

    I tried working with the formula above by putting 8,2*10^3N/400*10^6Pa*π and taking the square root of the answer in order to find r. I ended up with an answer(for r) of 0,0255 and that seems too small to be correct.

    I'm basically wondering about two things:

    Am I on the correct path with regards to the formula?
    Am I using the units correctly? (Pa vs N)
     
  2. jcsd
  3. Apr 11, 2013 #2

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    (Use adequate parentheses.)

    What are your units for the answer, 0.0255 ?

    Is that a diameter or a radius ?
     
  4. Apr 11, 2013 #3

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Also check the location of the decimal point in the answer.
     
  5. Apr 11, 2013 #4
    My bad, the answer would be for radius, r, so the diameter would be 2*r which would be 0,051.

    As for units, if the answer above is correct, the only thing that makes sense is that it's in meters, thereby giving a diameter of 5,1cm. (But, units, exponents etc. is something i really have to work on)
     
  6. Apr 11, 2013 #5

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Have you checked the location of the decimal point, as suggested by TSny ?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted