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: Moments and couples

  1. Feb 6, 2012 #1
    Could someone take a look at what I am working on and tell me if I am on the right track?

    #1: Determine the moment of the 200 N force about point B. Please see attached picture for FBD.

    First I find the x and y components.

    x = 100N y= 173.2N, which are perpendicular and parallel to AB.

    Then I find the distance of the 15° angle.

    sin15(.5) = 0.13m
    cos15(.5) = 0.48

    So, now I add the forces to determine the moment about point B.

    Mβ = +(173.2)(.48) - (100)(.13) = 70.1 N.M c.c.w

    It would be of great appreciation is someone could help me.
    Thank you.

    Attached Files:

  2. jcsd
  3. Feb 6, 2012 #2
    2: Says, replace the two 5 KN forces with an equivalent system consisting of the 7 KN force applied at C and a second force applied at point D. Determine the magnitude and direction of the second force and the distance CD.

    Please see the picture for the FBD.

    How I did this.

    First I found the moment about point O for the two 5 KN forces.

    Mo = -(5KN)(3m) + (5KN)(1.5m) = -7.5 KN.M c.w

    Then I found the x and y components for the 7 KN force.

    7(cos30) = 6.06 KN 7(sin30) = 3.5KN

    Next I placed the 6.06 KN and 3.5KN force at point D and solve the moment about point C,( Cancelling those forces) and rearranging for the distance CD.

    Mc = (3.5)(0) - (6.06)(d) = -7.5 KN.M

    d = -7.5 - (3.5)(0) / -6.06 = 1.24 m

    So, Magnitude = 6.06KN c.w. and CD = 1.24m

    Attached Files:

    • 7kn.png
      File size:
      8.2 KB
    Last edited: Feb 6, 2012
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook