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!

Calculating Moment

  1. Oct 7, 2007 #1
    1. It is known that the connecting rod AB exerts on the crank BC a 2.5kN force directed down and to the left along the center line of AB. Determine the moment of that force about C.

    [​IMG]




    2. cross product



    3.
    I found the angle using tan-1 = 144/42 = 73.7

    Fx = -2.5cos73.7 = -0.702
    Fy = -2.5sin73.7 = -2.40

    F = (-0.702i -2.40j + 0k)
    CB = (-42i -56j + 0k)


    F x CB= (-0.702i -2.40j + 0k) x (-42i -56j + 0k)
    = -61.5 kN mm

    does that seem right??????????????????????????

     
    Last edited: Oct 7, 2007
  2. jcsd
  3. Oct 7, 2007 #2
    that first was the vector approach but a scalar approach is


    y and x compents then multiply by distance and just add them

    Fx = 2.5 x cos 73.7 = 0.702
    Fy = 2.5 x sin 73.7 = 2.40

    Clockwise = -
    Counterclockwise = +

    Mx = -0.702 x 56
    My = 2.40 x 42

    M = Mx + My = 61.5 kN mm


    can someone make sure im interpreting the question accurately ! :)

    thanks!
     
  4. Oct 7, 2007 #3
    Anyone plzzzzzzzz
     
  5. Oct 8, 2007 #4
    no knows?
     
  6. Oct 8, 2007 #5

    Astronuc

    User Avatar

    Staff: Mentor

    I don't have a lot of time at the moment, but 73.7° is the angle of arm AB with respect to horizontal. Are you sure. The 2.5 kN acts through AB at angle of 16.3° with respect to vertical.

    To find the moment on BC, one wants the force component from AB normal to BC.
     
  7. Oct 8, 2007 #6
    hmmm huh? so what i did was wrong?...

    even if i use 16.3 basically the y component of the force AB is going to be

    -2.5cos16.3= which is what i found -2.40
    and x component
    -2.5sin16.3= -0.702

    these are the components of AB if i want moment about C i can take a vector from C to B and cross it with AB right?

    AB x CB = 61.5 kN mm
     
  8. Oct 8, 2007 #7
  9. Oct 8, 2007 #8
    can someone atleast explain properly what im doing wrong if im doing anything wrong...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Calculating Moment
  1. Moment calculation (Replies: 10)

  2. Moment calculation (Replies: 3)

  3. Moment calculation (Replies: 1)

Loading...