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!

Find tension in cables supporting giant swing

  1. Mar 4, 2016 #1
    1. The problem statement, all variables and given/known data
    Picture a seat that is supported by two cables. One is horizontal, and the other makes an angle of 40 degrees to the vertical. The swing swings in a horizontal circle at a rate of 32 rev/min. The horizontal cable is 7.5 m long. The person sitting on the seat at the end of the cables weighs 825N and the seat weighs 255N. What is the tension in each cable?

    2. Relevant equations
    see below

    3. The attempt at a solution
    I have worked out that;
    mv^2/r=F(horizontal)+F(slanted)sin40 i hat
    F(slanted)cos(40)=255+825 k hat

    My problem is that I feel as though i am not correctly determining the velocity, as I am not arriving at the correct answer. Here is my attempt:

    Radius to the centre of the circle: 7.5m
    circumference=2(pi)(radius)
    this gives me distance traveled in m.
    The swing moves 32 revolutions per min.
    therefore, 32x circumference is the total distance traveled per min
    multiply by 60 to get m/second.

    This number ends up getting way to huge! :(
     
  2. jcsd
  3. Mar 5, 2016 #2
    make out a free body diagram of the swing with the man sitting on it moving on circular path ; i think there will be two force equations; one in vertcal dir. another in horizontal direction!
     
  4. Mar 5, 2016 #3

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    You might want to think some more about that.

    Also, what value are you using for m in the horizontal force equation?
     
  5. Mar 5, 2016 #4
    I multiplied by 60 to get from from metres/min to metres/second. Can u explain whats wrong? thank :)
     
  6. Mar 5, 2016 #5
    I have done that :) K hat and I hat!
     
  7. Mar 5, 2016 #6

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    I can easily walk at 60 metres per minute. I have no chance of walking at 3600 metres a second.

    Edit: one way to get these conversions right is to treat the units as though they are variables.
    (60 m/min) / (60 sec/min) = ?
     
    Last edited: Mar 6, 2016
  8. Mar 5, 2016 #7
    well i did your calculation i get speed around 25 m/second thats not huge!
     
  9. Mar 5, 2016 #8

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Including "multiply by 60"?
     
  10. Mar 6, 2016 #9
    No, my 60 was in the denominator- Actually it has 32 rev. per minute so if i write rev per sec then it would be (32/60) rev per sec......
     
  11. Mar 6, 2016 #10

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    As I would hope.
     
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: Find tension in cables supporting giant swing
Loading...