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!

Mechanics Statics

  1. Oct 2, 2012 #1
    1. The problem statement, all variables and given/known data

    http://s11.postimage.org/yvt7eeg35/image.png [Broken]

    2. Relevant equations

    3. The attempt at a solution

    So I get that

    ƩFy = 0 = F(rod)y - F(weight)

    ƩFx = 0 = F(rod)x - F(spring)

    F(spring) = 200N * (1.5m + d)
    d being the unknown distance that the rod has moved by.

    So I get
    F(rod) = 60N / sinθ

    F(rod) = (200N * (1.5m + d)) / cosθ

    Which leaves me with 3 unknowns.
    d & θ & F(rod)

    But only 2 equations

    So I have no idea where to go from here
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Oct 2, 2012 #2

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    The equilibrium length of the spring is 1.5 m, so the force exerted by the spring is 200*d.

    There is another relationship available. How is d related to θ ?
     
    Last edited by a moderator: May 6, 2017
  4. Oct 2, 2012 #3
    So,

    cosθ = (1.5 - d) / 1.5

    sinθ = √(1.52 - (1.5 - d)2) / 1.5

    which would leave me with

    60 / √(1.52 - (1.5 - d)2) = 200d / (1.5 - d)

    What seems like a really hard problem to break down for d since to get rid of the square root I have to times everything then I'll end up with a d to powers of 1 2 3 and 4... I don't know how to solve that.

    I'm only 6 days in to this class.
     
  5. Oct 2, 2012 #4
    Remember, you can combine trigonometric expressions. You don't necessarily have to substitute in for both sin and cos.
    Also, you should have gone over solving higher degree polynomials in precalc. What's the highest math you've taken?
     
  6. Oct 2, 2012 #5

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Flip it over, square both sides.

    Maybe I'm not seeing something, but it looks like a quadratic equation to me.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Mechanics Statics
  1. Mechanics Statics (Replies: 2)

Loading...