Posted by **Aaron** on Sunday, February 12, 2012 at 3:30am.

A force F = 7^i + 6^j - 5^k lb. acts at the origin. Find the magnitude and

direction cosines of the moment of this force about point A (-4; 5; 6) ft

So in this case wouldn't

vector r= -4i +5j +6k

and

vector F = 7i + 6j - 5k lb?

and r X F = -61i +22j -59k = MA

[MA]= 87.67 ft-lbs

cosα = -61/87.67 => α=134°

cosß= 22/87.67 => ß=75.5°

cosγ= -59/87.67 => γ=132.3°

Not sure exactly where I went wrong because those angles don't make any sense.

- Engineering/Physics -
**drwls**, Sunday, February 12, 2012 at 5:46am
If the force acts at the origin, the lever arm r about point A is the opposite vector,

r = 4i -5j -6k

- Engineering/Physics -
**Aaron**, Sunday, February 12, 2012 at 2:21pm
Ah, I knew there must be something off about my answer.

Thank you so much!!!

## Answer this Question

## Related Questions

- physics - A force 1 of magnitude 5.40 units acts at the origin in a direction ...
- Engineering - A force of 26 lb. acts through a point (4; 5; -7) ft. and is ...
- Physics - A force 1 of magnitude 7.20 units acts on an object at the origin in a...
- physics - A force Farrowbold1 of magnitude 5.00 units acts on an object at the ...
- physics - A force in the +y direction applied at the point x=2.3m,y=1.4m gives ...
- physics - A particle has a charge of +1.5 µC and moves from point A to point B, ...
- physics - A particle has a charge of +1.5 µC and moves from point A to point B, ...
- Physics - A force of 20 N acts toward the west. Another force acts at the same ...
- Physics - A coin slides over a frictionless plane and across an xy coordinate ...
- Physics - A coin slides over a frictionless plane and across an xy coordinate ...