This preview shows page 1. Sign up to view the full content.
11.94:
a) Taking torques about the point where the rope is fastened to the
ground, the lever arm of the applied force is
2
h
and the lever arm of both the
weight and the normal force is
.
tan
)
(
so
and
,
tan
2
θ
h
w
n
F
h
h

=
Taking torques
about the upper point (where the rope is attached to the post),
.
2
h
F
h
f
=
Using
n
f
s
μ
≤
and solving for
F,
,
400
36.9
tan
1
30
.
0
1
)
400
(
2
tan
1
1
2
1
1
s
nN
nN
w
F
=
°

=

≤


b) The above relations between
become
and
,
f
n
F
,
5
2
,
tan
)
(
5
3
F
f
h
w
n
h
F
=

=
and eliminating
gives
for
solving
and
and
F
n
f
,
tan
5
3
5
2
1
s


≤
w
F
and substitution of numerical values gives 750 N to two figures. c) If the force is
This is the end of the preview. Sign up
to
access the rest of the document.
Unformatted text preview: applied a distance y above the ground, the above relations become , ) ( , tan ) ( fh y h F h w n Fy == which become, on eliminating , and f n ( 29 ( 29 . tan 1 s ≥ h y h y F w As the term in square brackets approaches zero, the necessary force becomes unboundedly large. The limiting value of y is found by setting the term in square brackets equal to zero. Solving for y gives . 71 . 36.9 tan 30 . 9 . 36 tan tan tan = ° + ° = + = s h y...
View
Full
Document