How Does FGF sin26.6 Generate Moment About Point D in Truss Analysis?

[fonseh]

Homework Statement

For moment about D , how could the FGF sin26.6 generate moment about D ?

Homework Equations

The Attempt at a Solution

FGF sin26.6 is located above point D , right ? How could FGF sin26.6 generate moment about D ?

 

[haruspex]

If calculating moments by first breaking the force into components then you have to select a point of application of the force. Anywhere in the line of action will do. In this case you can use G, F or O.
If you use G there will be a clockwise moment about D from the horizontal component and an anticlockwise moment from the vertical component.
If you select F, only the horizontal component will have a moment about D, but it will be less than that of the horizontal component at G.
If you select O, as the author has done, only the vertical component has moment about D.

 

[fonseh]

If calculating moments by first breaking the force into components then you have to select a point of application of the force. Anywhere in the line of action will do. In this case you can use G, F or O.
If you use G there will be a clockwise moment about D from the horizontal component and an anticlockwise moment from the vertical component.
If you select F, only the horizontal component will have a moment about D, but it will be less than that of the horizontal component at G.
If you select O, as the author has done, only the vertical component has moment about D.

S

If calculating moments by first breaking the force into components then you have to select a point of application of the force. Anywhere in the line of action will do. In this case you can use G, F or O.
If you use G there will be a clockwise moment about D from the horizontal component and an anticlockwise moment from the vertical component.
If you select F, only the horizontal component will have a moment about D, but it will be less than that of the horizontal component at G.
If you select O, as the author has done, only the vertical component has moment about D.

Ok , i can understand what you have explained . But for this type of question ,
how do we choose the point of application of force ? It's not stated in the question . Choosing different point of application of forces will yield different answer

 

[haruspex]

Choosing different point of application of forces will yield different answer

No, as long as the points are along the line of action they will all yield the same answer.