EXAMPLE 5.0.9: RESULTANT MOMENT OF SPATIAL FORCES

Two cables are hooked at points B and C to keep a flagpole upright. With tensile forces of 780N and 420N for forces B and C respectively, determine the resultant moment produced about point O.

The procedure of taking the resultant of moments for the spatial forces would still follow the same principle that resultant is the summation of moments. 

                                        

Solve for the moment of each force about point O and take the resultant by computing the summation of moments. Similar with the previous examples, each moment can be determined using two points, both of which still yield the same value.

FOR MOMENT OF FB:

The two ways to determine this moment is either by:

                     or      

The use of position vector at A for illustration purposes:

                                        

Force B in its vector form is

                                       

                                       

Taking the moment of Force B about point O

             

              

               


FOR MOMENT OF FC:

The two points to consider for the position vector involving Fc are points A and C. Let us use point A as it is already readily available from force B's position vector.

                                           

Force C in its vector form is

                

               

So the moment of Fc about point O is

               

              

             


FOR RESULTANT MOMENT ABOUT POINT O

                                       ANSWER

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