COSMOS: Complete Online Solutions Manual Organization System
Chapter 4, Solution 130.
Free-Body Diagram:
Express forces and moments in terms of rectangular components:
FDE = FDE
− 40 i − 70 j + 40k
( − 40 )
2
2
+ ( − 70 ) + ( 40 )
2
=
FDE
(− 4i − 7 j + 4k )
9
FA = ( 24 N )( sin 20° i − cos 20° j)
B = By j + Bzk ,
(a) ΣFx = 0:
M B = M By j + M Bzk
4
− FDE + 24sin 20° = 0
9
FDE = 18.4691 N
ΣM B = 0:
or
FCF
or FDE = 18.47 N
rBC × FCF + rBD × FDE + rBA × FA + M B = 0
i
j k
i
j k
i
j
k
18.4691
−1 + M B y j + M B zk
0 − 48 36 +
0 − 80 60 + ( 80 )( 24 ) 0
0
9
0 −1 0
−4 −7 4
sin 20° − cos 20° 0
continued COSMOS: Complete Online Solutions Manual Organization System
Equating the coefficients of the unit vectors to zero:
i:
36FCF +
18.4691
(100 ) + (80 )( 24 )( − cos 20° ) = 0
9
FCF = 44.417 N
or FCF = 44.4 N
(b)
j:
18.4691
( − 240 ) + (80 )( 24 )( − sin 20° ) + M By = 0
9
M By = 1149.19 N ⋅ mm
k:
18.4691
( − 320 ) + M Bz = 0
9
M Bz = 656.68 N ⋅ mm
ΣFy = 0:
By − 44.417 −
7
(18.4691) − 24 cos 20° = 0
9
By = 81.3 N
ΣFz = 0:
Bz +
4
(18.4691) = 0
9
Bz = −8.21 N
Therefore:
B = ( 81.3 N ) j − ( 8.21 N ) k
M B = (1.149 N ⋅ m ) j + ( 0.657 N ⋅ m ) k
COSMOS Chapter 4 Solution 130
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