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: Conceptual center of mass question - No calculations

  1. Apr 28, 2010 #1
    1. The problem statement, all variables and given/known data
    In using a ladder where the wall is smooth but the floor has a coefficient Us, why is it necessary to make the angle large?


    2. Relevant equations
    p11-78alt.gif


    3. The attempt at a solution

    I'm a little confused by this, because I would think that you would want to make the angle smaller and have the center of mass be lower. What is the benefit of the ladder being more vertical?
     

    Attached Files:

  2. jcsd
  3. Apr 28, 2010 #2

    rock.freak667

    User Avatar
    Homework Helper

    Is the question specifically asking why to make the angle larger? Because normally, your reasoning would be correct.
     
  4. Apr 28, 2010 #3
    Here is the exact problem as my professor wrote it. i didn't post it before, because frankly... His handwriting is impossible to decipher. Im just confused because the mass of the person makes the center of mass EVEN higher. I see no reason why increasing the angle is beneficial.

    9308e978367172.gif
     
  5. Apr 29, 2010 #4

    rock.freak667

    User Avatar
    Homework Helper

    Well it seems that if you sum the moments about the point where it touches the bottom, the moments will depend on cosθ. But this is assuming the the center of mass of the person is directly on the ladder.


    EDIT: I forgot about the other normal force. To be honest, I really don't see how increasing that angle will make it more stable.
     
  6. Apr 29, 2010 #5
    Try looking at the torque produced by the mg-force and the normal force from the wall with respect to the point of contact on the ground. What happens if the angle increases/decreases?

    The R.D. Werner Ladder Co. recommends that its ladders be used at an angle of 75 degrees.
     
    Last edited: Apr 29, 2010
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook