Find the moment about the and axis

[Colts]

1. Homework Statement
http://session.masteringengineering...bs._454_55.jpg
Find the moment about the axis AC. F=<7,12,-6>


2. Homework Equations
MomentAC = Uac dotted with (Rab X F)
Uac is the unit vector from a to c


3. The Attempt at a Solution
Uac=<.8,.6,0>
Rab=<4,3,-2>
F=<7,12,-6>
Rab X F =<6,-10,0>
MomentAC=4.8-6
=-1.2
MomentAC*Uac=<-.96,-.72,0>

 

[voko]

The link to the picture is garbage.

 

[Colts]

Sorry. This should work
http://session.masteringengineering.com/problemAsset/1127287/7/Probs._454_55.jpg

 

[voko]

How did you compute Rab x F? I get a different result.

 

[Colts]

(-6(3)-(-2)12)-(-6(4)-7(-2))+(7(12)-7(3))
(-18+24)-(-24+14)+(48-21)
6,10,27

 

[voko]

This is different fro what you had before, and this is what I get as well. You just need to do the scalar product now.