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: Distance Force Calculation

  1. Nov 9, 2008 #1
    1. The problem statement, all variables and given/known data
    A steel beam that is 6.50 m long weighs 354 N. It rests on two supports, 3.00 m apart, with equal amounts of the beam extending from each end. Suki, who weighs 535 N, stands on the beam in the center and then walks toward one end. How close to the end can she come before the beam begins to tip?

    2. Relevant equations

    unsure what to use

    3. The attempt at a solution

    This problem is confusing for me, I tried drawing a picture and am unsure if it is correct, so I have no idea how to solve this or attempt this in a correct way
  2. jcsd
  3. Nov 9, 2008 #2


    User Avatar
    Homework Helper

    Draw a picture.

    Now choose either support as a pivot point.

    On one side you have the center of mass of that part of the beam acting over its distance to the pivot. On the other side you have Suki and the center of mass of the other side of the beam. The moment little Suki slides past the distance to maintain balance is where it all comes apart doesn't it?
  4. Nov 9, 2008 #3
    So I "split" the beam in half so the left side would be
    177N and the other half with Suki would be 712N

    How would i go from there?
  5. Nov 9, 2008 #4


    User Avatar
    Homework Helper


    You need to split the weight of the beam between each side of the pivot point. The center is not the pivot point. You need to calculate where the support point that it will pivot about is on the beam first. Then divide the weight between the 2 sides.

    But even after you find the weight division you still need to find the center of mass for each of those sides of the beam.

    Suki*distance + part beam center of mass*distance = other part beam center of mass*distance.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook