830 × / D ENGR 141 Class , 2 Skills Asix tps://ualearn.blackboard.com/bbcswebdav

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830 × / D ENGR 141 Class , 2 Skills Asix tps://ualearn.blackboard.com/bbcswebdav/pid-361 7063-dt-content-rid-322 10349_1 /courses/ 30936.201830/ENGROS20103% Homework Attendance July 31 s ft 2 ft 4 ft 3 ft 6 ft 2 ft 5 f Find a position vector from B to D If the force in cable BD has magnitude 86.3 lbf, then write a cartesian form vector for force BD Calculate the moment of that force about point A using position vector FAB 8 ft i Calculate the moment of that force about point A using position vector FAD 0 ft i+ 4 ft j - 8 ft k THE UNIVERSITY OF ALABAMA 3 4 8 0

Explanation / Answer

POsition vector from B to D.

BD = (0 , 4, -8) - (8, 0 , 0)

BD = -8 i + 4j - 8k ..........Ans

F = 86.3 lbf

force BD = (F)(BD) / |BD|

= (86.3 lbf) (- 8i + 4j - 8k) / sqrt(8^2 + 4^2 + 8^2)

F = - 57.5 i + 28.8 j - 57.5 k lbf ........Ans

moment = r x F

= (8i) x (- 57.5 i + 28.8 j - 57.5 k)

= 230 k + 460 j

Ans: 0i + 460j + 230 k lbf-ft

moment = (0i + 4j - 8k) x (-57.5i + 28.8j - 57.5 k)

= 230 k - 230 i + 460 j + 230i

Ans: 0i + 460j + 230 k lbf-ft  

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