COSMOS: Complete Online Solutions Manual Organization System
Chapter 4, Solution 151.
Free-Body Diagram:
(a) The location of D follows from the geometry of the problem. Since the steel plate is rectangular rD/ A is
perpendicular to rB/ A and therefore:
rD/ A ⋅ rB/ A = 0
Denoting the coordinates of D by (0, y, z):
rD/ A = − ( 0.1 m ) i + yj + ( z − 0.7 m ) k
rB/ A = ( 0.3 m ) i − ( 0.4 m ) k
and
Thus, rD/ A ⋅ rB/ A = − 0.03 − 0.4 z + 0.28 = 0
or
z = 0.625 m.
rD/ A =
( − 0.1 m )2 +
2
y 2 + ( 0.625 m − 0.7 m ) = 0.75 m
continued COSMOS: Complete Online Solutions Manual Organization System
Solving for y:
y = 0.73951 m
x = 0, y = 0.740 m, z = 0.625 m
Location of D is therefore:
(b) Consider moment equilibrium about axis AB:
λ AB
uuur
AB
=
=
AB
0.3i − 0.4k
( 0.3)2 + ( − 0.4 )2
= 0.6i − 0.8k
rD/ A = − ( 0.1 m ) i + ( 0.73951 m ) j − ( 0.075 m ) k
rD/B = − ( 0.4 m ) i + ( 0.73951 m ) j + ( 0.625 m − 0.3 m ) k
N D = N Di
(
)
W = − ( mg ) j = − ( 40 kg ) 9.81 m/s 2 j = − ( 392.4 N ) j
Then,
ΣM AB = 0:
(
)
(
)
λ AB ⋅ rD/ A × N D + λ AB ⋅ rG/B × W = 0
− 0.8
−0.8
0.6
0
0.6
0
− 0.1 0.73951 − 0.075 + − 0.2 0.36976 0.1625 = 0
− 392.4
ND
0
0
0
0
0.59161 N D − 24.525 = 0
N D = 41.455 N
or N D = ( 41.455 N ) i
COSMOS Chapter 4 Solution 151
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