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!

Ladder - Equilibrium

  1. Nov 2, 2008 #1
    1. The problem statement, all variables and given/known data


    A uniform 5.0-kg ladder is leaning against a frictionless vertical wall, with which it makes a 15* angle. The coefficient of friction between ladder and ground is 0.26. Can a 65-kg person climb to the top of the ladder without it slipping? If not, how high can the person climb? If so, how massive a person would make the ladder slip?

    2. Relevant equations
    \sum {\vec \tau } = \vec 0 \hfill \\
    \sum {\vec F} = \vec 0 \hfill \\

    3. The attempt at a solution

    So, I choose the end of ladder that is touching the floor to be the axis. Now I want to find the sum of the torques, then set them equal to zero. What I don't quite get in the equation is the sin(90-15) in the first term in the following equation my professor gave me:

    F_W L\sin (90^ \circ - 15^ \circ ) - M_p gL\sin (15^ \circ ) - M_L g\frac{L}
    {2}\sin (15^ \circ ) = 0

    sin(90-15)? Technically, it should be the angle between the r and F....but this doesn't make sense to me....or perhaps 15* is meant to be the other angle in the triangle?

    If anyone can help, it would be greatly appreciated. Thank you!
    Last edited: Nov 2, 2008
  2. jcsd
  3. Nov 3, 2008 #2


    User Avatar
    Homework Helper

    Hi RedBarchetta,

    Yes, it's the other angle; the ladder makes a 15 degree angle with the wall, so the angle with the floor is 75 degrees. Once you correct your diagram, do you see why the angles your professor chose are correct?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Ladder - Equilibrium
  1. Ladder Problem (Replies: 6)

  2. Ladder Problem (Replies: 3)

  3. Student on Ladder (Replies: 1)

  4. Sliding Ladder (Replies: 5)

  5. Force on a ladder (Replies: 8)