# Statics- Resultant couple moment

## Homework Statement

If F_1 = 100N , F_2 = 120N and F_3 = 80N , determine the magnitude and coordinate direction angles of the resultant couple moment.

M=Fd
M=r x F
MR=Ʃ(r x F)

## The Attempt at a Solution

I found the couple moment for each force:
M1=F1d=100(0.2) or (-20j using right hand rule)
M2=F2d=120(0.2) or +24i
M3=F3d=80(0.2) or -16k
M4=this is what im having problems with...not sure how to get the moment for F4... if do 150(.3)(cos30)=38.97 i get the wrong resultant.

The correct answer should be (MC)R=71.9 Nm...
Any help would be greatly appreciated.

#### Attachments

• Hibbler_ch4_p95.jpg
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tiny-tim
Homework Helper
hi rico22! The correct answer should be (MC)R=71.9 Nm...

i don't get 71.9 unless i use .33 instead of .3 TSny
Homework Helper
Gold Member
Note that the F4 couple is not in the x-direction. It is parallel to the xy plane but it has both x and y components which you will need to work out.

• 1 person
tiny-tim
ooh, i didn't notice that! i read the axis of that pipe, and the short line above the positive x-axis, as one continuous straight line! yes, now i get 71.9 … thanks, Tsny 