1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Giant Swing

  1. Oct 21, 2015 #1
    1. The problem statement, all variables and given/known data
    In one of the versions of the "Giant Swing", the seat is connected to two cables, one of which is horizontal (Figure 1) . The seat swings in a horizontal circle at a rate of 33.0 rev/min .

    If the seat weighs 295 N and a 869-N person is sitting in it, find the tension in the horizontal cable.

    2. Relevant equations
    Period=circumference/velocity so 2πR/v

    3. The attempt at a solution
    I drew two FBD(free body diagrams). One for the person and one for the chair
    For the person : TsinΘ-W-Fn=0
    Fn = Weight of the chair

    For the chair: Th+TcosΘ=mv2/r
    Th = mv2/r - TcosΘ
    mv2/r - [(Wc + Wp)/sinΘ]*cosΘ

    To get the velocity, we use period = circumference /velocity
    33 rev/min * 1min/60 sec = 0.55 rev/sec
    0.55 = 2π(7.5)/v
    m= (Wp + Wc)/9.8
    So (Wp+Wc/9.8)(81.68)2/7.5 - (295+869)/tan40

    Basically I end up getting a huge number and I'm fairly certain that it's wrong but can't see why
  2. jcsd
  3. Oct 21, 2015 #2


    User Avatar
    Homework Helper

    I haven't checked your work in detail (sorry) but you should be able to treat the person and chair as a single object. The vertical component of the tension in the slanted cable must balance the weight of the person+chair, and the horizontal components of the two tensions must provide the centripetal acceleration.
  4. Oct 21, 2015 #3
    yea that's basically what I did. I guess my main problem is I don't know how to convert rev/min to m/s so I just took the rev/min and divided it by 60 to get rev/sec which gives 0.55rev/sec

    I then took 2π(7.5)/0.55 to get velocity. Wondering if that step is correct
  5. Oct 21, 2015 #4


    User Avatar
    Homework Helper

    ##2\pi\frac{\text{radians}}{\text{revolution}}\cdot 7.5\frac{\text{meters}}{\text{radian}}\cdot\frac{1}{0.55\frac{\text{revolutions}}{\text{second}}}##

    Check the units in the above equation. If it is not meters/second then try to fix it so it is.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted