Components of the equivalent moment at a point

  • #1
Davidf77
1. The problems:
Screen Shot 2017-09-21 at 5.34.33 PM.png
Screen Shot 2017-09-21 at 5.34.45 PM.png
Screen Shot 2017-09-21 at 5.34.33 PM.png
Screen Shot 2017-09-21 at 5.34.45 PM.png

Screen Shot 2017-09-21 at 5.34.33 PM.png
Screen Shot 2017-09-21 at 5.34.45 PM.png


The questions are to find the x, y and z components of the equivalent MOMENT at point A in both diagrams.

For the green block, I found the y and z components of the equivalent force at point A are -39.04kN and 15.48kN respectively.

The Attempt at a Solution



For the first question (the green block) I attempted to find a solution by crossing the unit vectors with the forces at each place the force is acting on. Then I subtracted 75 from the x component due to the moment of 75kN-m. I found the x component to be 26.836kN-m, the y to be 9.68kN-m, and the z to be 234.24kN-m. These are all wrong. I tried summing moments several different ways and every way I tried was wrong.

For the second question (the blue thing) I used the same approach as the last one, crossing the unit vectors with the forces at each place the force is acting on. I got 1300N-mm for the x component, 127800N-mm for the y component, and -40200N-mm for the z component. These are all wrong as well.

There is a third question that is the same concept as these two and I used the same approach for that and my answers for that one were all correct, so I don't know what I am doing wrong for these two.
 
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  • #2
Davidf77 said:
found the x component to be 26.836kN-m,
That is not what I get. Please post the details of your working.
 
  • #3
haruspex said:
That is not what I get. Please post the details of your working.

Yeah I know that's wrong. This is my work, I just really can't figure it out
IMG_1821.JPG
IMG_1820.JPG
 
  • #4
Davidf77 said:
Yeah I know that's wrong. This is my work, I just really can't figure it out
View attachment 211537View attachment 211538
That's too messy.
My response singled out one datum, the x component you calculated for the torque on the green block. Please post just your calculation of that, taking the trouble to type your working in, not uploading an image.
(Images are for textbook extracts and diagrams.)
 

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