978-0073380292 Chapter 9 Part 4

subject Type Homework Help
subject Pages 14
subject Words 4865
subject Authors Francesco Costanzo, Gary Gray, Michael Plesha

Unlock document.

This document is partially blurred.
Unlock all pages and 1 million more documents.
Get Access
page-pf1
page-pf2
Statics 2e 1391
Problem 9.46
The structure consists of two uniform members AB and BC, each weighing
2kN
.
The members are pinned to one another at
B
, and the structure is supported
by surfaces at
A
and
C
having coefficients of static friction of 1.2 and 0.5,
respectively. Determine the largest positive value Pthe structure can support.
3)PD 0:5000 kN:(13)
page-pf3
Problem 9.47
The structure consists of two uniform members AB and BC, each weighing
2kN
and
P0
. Determine the minimum coefficient of static friction needed
at surface
A
and the minimum coefficient of static friction needed at surface
C
so that neither surface slips for any value of P(this is called self-locking).
page-pf4
page-pf5
Problem 9.48
A wrench is used to twist a pipe
C
. The wrench consists of jaw BD and handle-
jaw
ADE
, with a pin at
D
. The coefficient of static friction
s
for all contact
surfaces is the same. Determine the minimum value of
s
so that there is no
slip at Aor Bregardless of the value of force P(this is called self-locking).
Solution
The FBDs shown at the right have the directions of friction forces
F1
and
F2
such that if slip occurs at point
A
, then point
A
will move downward
relative to the fixed pipe, and if slip occurs at point
B
, then point
B
will
move upward relative to the fixed pipe.
page-pf6
Problem 9.49
A small lamp is clamped on a fixed circular bar
C
. The lamp assembly weighs
4lb
with center of gravity at point
G
, and the weights of all other members are
negligible. Determine the minimum moment the torsional spring at
D
must
produce so the lamp does not slip on the bar. The contact surfaces at
A
and
B
have coefficients of static friction of AD0:25 and BD0:35.
page-pf7
(7) and (10). Hence,
page-pf8
Problem 9.50
A bracket
ABCDEF
is clamped to a fixed circular bar. The bracket consists
of a horizontal member
ABC
that is pinned at
C
to member
CDEF
, and a
vertical bolt
BD
. The force
P
at point
F
is vertical, and the bracket makes
contact with the fixed bar at points
A
,
G
, and
E
. If all contact surfaces have the
same coefficient of static friction of 0.4, and if
PD50 lb
, determine the force
that bolt BD must support to prevent slip.
page-pf9
page-pfa
Problem 9.51
Two objects are connected by a weightless cord that is wrapped around a fixed cylindrical
surface. The coefficient of static friction between the cord and surface is 0.3. One of the
objects weighs
100 lb
, and the other has weight
W
. If the system is initially at rest, determine
the range of values for Wfor which there is no motion.
page-pfb
Problem 9.52
A
10
N weight is supported by a weightless cable where portion
AB
of the cable is
horizontal. The coefficients of static and kinetic friction are 0.5.
(a)
Determine the value of
P
so that downward motion of the
10
N weight is impend-
ing.
(b)
If
PD3
N, determine the force in portion CD of the cable. Is the system in
equilibrium or is there motion? Explain.
page-pfc
Problem 9.53
A
10
N weight is supported by a weightless cable where portion
AB
of the cable is
horizontal. A test is conducted where it is found that
PD4
N will cause impending
motion of the 10 N weight at D.
(a)
Determine the coefficient of static friction between the cable and cylindrical
surface.
(b)
Determine the tension in portion
BC
of the cable as a function of angular position
. Plot this function.
page-pfd
Problem 9.54
A hoist for lifting lightweight building materials is shown. The pulley at
B
is frictionless, and the pulley at
C
is driven by an electric motor rotating
counterclockwise at a speed high enough to always cause slip between the
cable and pulley
C
. The cable makes contact with one-fourth of the surface
of pulley
C
, and the coefficients of static and kinetic friction are 0.25 and 0.2,
respectively. If the cable has negligible weight and the building materials and
platform at
D
have a combined weight of
100 lb
, determine the force the worker
must apply to the cable to
(a) Raise the building materials at a uniform speed.
(b) Lower the building materials at a uniform speed.
(c) Hold the building materials in a fixed, suspended position.
page-pfe
Problem 9.55
In Prob. 9.54, if the cable were given an additional full wrap around the pulley
at
C
and if the worker can apply a force of
50 lb
to the cable, determine the
largest weight that may be lifted at D.
page-pff
Problem 9.56
The machine shown is used to slowly lower and raise the object at point
D
.
Cable
BCD
is wrapped around the drum at
B
a large number of turns, and
cable segment
BC
is horizontal. The coefficients of static and kinetic friction
are 0.22 and 0.18, respectively. Let
P
be the force the operator applies to
point
A
of the machine, where this force is perpendicular to the crank
AB
. If
WD20 lb
, determine the range of values for
P
so that there is no motion of
the object at D.
page-pf10
Problem 9.57
In Prob. 9.56, if the person operating the machine can apply a maximum force
of
25 lb
to the handle
A
of the machine, where this force is perpendicular to the
crank
AB
, and if the cable has
50 lb
strength, determine the largest value of
W
that may be lowered, and the largest value of
W
that may be raised. Hint:
Lowering and raising motions will be initiated from at-rest conditions.
page-pf11
page-pf12
Problem 9.58
A brake for reducing the speed of a rotating drum is shown. The braking
moment is defined as the resultant moment the belt produces about the drum’s
bearing, point
A
. Determine the braking moment if the coefficient of kinetic
friction is 0.35 and: The drum rotates clockwise and PD90 N.
MADT2.20 cm/T1.20 cm/(6)
page-pf13
Problem 9.59
A brake for reducing the speed of a rotating drum is shown. The braking
moment is defined as the resultant moment the belt produces about the drum’s
bearing, point
A
. Determine the braking moment if the coefficient of kinetic
friction is 0.35 and: The drum rotates counterclockwise and PD90 N.
MADT2.20 cm/T1.20 cm/(6)
page-pf14
Problem 9.60
0.35 and: The drum rotates clockwise and PD20 lb.
MADT2.10 in:/ T1.10 in:/ (7)

Trusted by Thousands of
Students

Here are what students say about us.

Copyright ©2022 All rights reserved. | CoursePaper is not sponsored or endorsed by any college or university.