COSMOS: Complete Online Solutions Manual Organization System
Chapter 3, Solution 129.
First, reduce the given force system to a force-couple system at the origin.
Have
ΣF :
( 2P ) i − ( P ) j + ( P ) j = R
∴ R = ( 2P ) i
Have
ΣM O : Σ ( rO × F ) = M OR
M OR
i j k
i j k
= Pa 2 2 2.5 + 0 0 4 = Pa ( −1.5i + 5j − 6k )
2 −1 0
0 1 0
R = 2Pi
(a)
or Magnitude of R = 2P
Direction of R : θ x = 0°, θ y = −90°, θ z = 90°
(b) Have
M1 = λ R ⋅ M OR
λR =
R
R
= i ⋅ ( −1.5Pai + 5Paj − 6Pak )
= −1.5Pa
and pitch
.
P=
M1
−1.5Pa
=
= −0.75a
R
2P
or P = −0.75a COSMOS: Complete Online Solutions Manual Organization System
M OR = M1 + M 2
(c) Have
∴ M 2 = M OR − M1 = ( 5Pa ) j − ( 6Pa ) k
Require
M 2 = rQ/O × R
( 5Pa ) j − ( 6Pa ) k = ( yj + zk ) × ( 2Pi ) = − ( 2Py ) k + ( 2Pz ) j
From
i : 5Pa = 2Pz
∴ z = 2.5a
From
k : − 6Pa = −2Py
∴ y = 3a
∴ The axis of the wrench is parallel to the x-axis and intersects the yz-plane at y = 3a, z = 2.5a
.
COSMOS Chapter 3 Solution 129
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