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: Moment in a beam

  1. May 5, 2015 #1

    I am calculating the all reaction forces in this beam.
    However, I want to ask:
    By taking moment about point B, why does the moment of the UDL become 15*7*5.5 instead of 15*7*4.5

    Thanks !
    Last edited by a moderator: May 5, 2015
  2. jcsd
  3. May 5, 2015 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    It's not clear where the 4.5 is measured from in the second expression.

    The UDL is a constant 15 kN/m applied over a distance of 7 meters in total, therefore, the center of this load is 3.5 meters from either the LHS or the RHS of the UDL.
    By taking point B as the moment reference, the moment of the UDL becomes 15 kN/m * 7 meters * (2 + 3.5) meters, where 2 + 3.5 = 5.5 meters is the distance from point B to the center of the UDL.
  4. May 5, 2015 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    When determining the moment of a distributed load about a point, you may find the moment by replacing the distributed load with a resultant concentrated load acting at the cg of the load distribution. Where is the cg of that load located along its 7 foot length?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted