COSMOS: Complete Online Solutions Manual Organization System
Chapter 4, Solution 85.
Free-Body Diagram:
(a)
Using the law of cosines on triangle ABC:
2
2
R 2 = ( 2R ) + ( 2R ) − 2 ( 2R )( 2R ) cosθ
1 = 8 − 8cosθ
7
8
θ = 28.955°
Also,
cosθ =
2R cos (θ + α ) = R cos α
2R ( cosθ cos α − sin θ sin α ) = R cos α
tan α =
2 cosθ − 1 2cos 28.955° − 1
=
2 sin θ
2 sin 28.955°
or α = 37.8°
α = 37.761°
(b)
From the free-body diagram:
2R
R
=
sin φ sin θ
sin φ = 2sin θ = 2 sin 28.955°
φ = 75.522°
Now using the law of sines on the force triangle:
NA
NB
W
=
=
sin [90° − (φ − α )] sin 90° − (θ + α ) sin (θ + α ) + (φ − α )
NA
NB
mg
=
=
cos(φ − α ) cos (θ + α ) sin (θ + φ )
NA
NB
mg
=
=
cos 37.762° cos 66.716° sin104.478°
Solving for N A and N B :
N A = 0.816 mg
N B = 0.408 mg
66.7°
37.8°
COSMOS Chapter 4 Solution 85
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