COSMOS: Complete Online Solutions Manual Organization System
Chapter 3, Solution 136.
First reduce the given force-couple system to an equivalent force-couple system ( R, M B ) at point B.
d BD =
( − 480 mm )2 + ( 560 mm )2 + ( − 480 mm )2
= 880 mm
FBD = FBDλBD =
132 N
( − 480i + 560 j − 480k )
880
= (12 N )( − 6i + 7 j − 6k )
d EB =
( 240 mm )2 + ( − 220 mm )2 + ( 480 mm )2
= 580 mm
FEB = FEBλEB =
145 N
( 240i − 220 j + 480k )
580
= ( 5 N )(12i − 11j + 24k )
ΣF :
R = FBD + FEB
= (12 N )( − 6i + 7 j − 6k ) + 5 N (12i − 11j + 24k )
= − (12 N ) i + ( 29 N ) j + ( 48 N ) k
d BF =
( 340 mm )2 + ( 240 mm )2 + ( − 60 mm )2
= 20 442 mm
Then
MB =
=
.
20 N ⋅ m
( 340i + 240 j − 60k )
20 442
20 N ⋅ m
(17i + 12 j − 3k )
442 COSMOS: Complete Online Solutions Manual Organization System
Now determine whether R and M B are perpendicular
R ⋅ M B = ( −12 j + 29 j + 48k ) ⋅
20
(17i + 12 j − 3k )
442
20
( −12 × 17 + 29 × 12 − 48 × 3)
442
=
=0
∴ R and M B are perpendicular so that ( R, M B ) can be reduced to the single equivalent force
R = − (12.00 N ) i + ( 29.0 N ) j + ( 48.0 N ) k
Now require M B = rB/P × R
or
j:
20 × 12
= −12 ( z − 0.480 ) + 0.480 ( 48 )
442
or
k:
i
j
k
20 N ⋅ m
(17i + 12 j − 3k ) = − 0.480 y z − 0.480 ( N ⋅ m )
442
−12 29
48
z = 1.449 m
− 20 × 3
= − 0.480 ( 29 ) + 12 y
442
or
y = 0.922 m
∴ The point of intersection is defined by
y = 0.922 m
z = 1.449 m
.
COSMOS Chapter 3 Solution 136
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