Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Equilibrium help !

  1. Nov 11, 2005 #1
    Equilibrium help plz!

    Hi, I'm having problems with one of my homework assignments on equilibrium. I'm fine with all the calculations once I draw up a free body diagram but I'm not particulary good at visualizing the problem etc. :confused: Can anyone help me out with the diagram?

    The question is:

    A block of mass m is lying on a rough table, the coefficient of friction being µ. One end of an elastic string of modulus λ and natural length l is attached to the block. The other end of the string is pulled in a direction away from the block so that the string is at an angle of 45° to the horizontal.

    Thanks for reading!
  2. jcsd
  3. Nov 11, 2005 #2


    User Avatar
    Homework Helper

    Sigh. The preformatted text tag doesn't work. I think I knew that.

    The string is pulling the block both to the side and upwards at a 45 degree angle. This will give you not only a force tending to make the block slide but one pulling it upward from the table, reducing the normal force exerted on the block by the table (and, via N3, vice versa, of course).

    Does that help?
  4. Nov 11, 2005 #3
    hmm I know what you are getting at...but I'm still unsure of how to present the diagram :frown:

    What would it look like if it was just a normal sketch of a block with the string? I seem to find it easier to construct the free body diagrams with an initial diagram without the complicated forces.
  5. Nov 11, 2005 #4


    User Avatar
    Homework Helper

    Well, the only difference is that 45 degree angle. If it weren't for that, you'd have the force of the string one way, the force of friction the other, the normal force up and weight down.
    As the problem stands, you still have those forces except that the force of the string needs to be broken into components, one vertical and one horizontal.
  6. Nov 13, 2005 #5
    I get it nowz, thanks for your help! :D
    Last edited: Nov 13, 2005
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook