Statics 2e 899
Problem 6.69
Imagine you have been retained by an attorney to serve as an expert witness
for possible litigation regarding an accident that occurred on the playground
structure shown. You have been given only preliminary information on this
structure, including the following:
It was designed as a truss structure.
It had been in service for several years, without incident.
It collapsed while an adult was climbing on it, causing serious injury to
the person.
It was thought to be in good condition at the time of the accident.
Detailed information on the design, fabrication, installation, and so forth
has not yet been made available to you.
Until you have fully studied all of the information available, it is not possible
for you to render an informed opinion on this structure and/or the accident that
occurred. Nonetheless, the attorney retaining you is anxious to informally hear
your initial impressions. With the information provided, what would you tell
the attorney? In answering this, consider responses such as: the structure may
have been defective in its design, it may have been defective in its fabrication or
installation, the adult probably should not have been on the structure and thus,
he or she is probably responsible for its failure, or I really don’t know until I
have further information.
Problem 6.70
The truss shown has a socket support at point
L
, a
roller at point
K
, and a cylindrical roller at point
A
that prevents motion in the
x
and
´
directions.
Determine if the truss is statically determinate or
statically indeterminate.
Problem 6.71
The truss shown has a socket support at point
L
, a
roller at point
K
, and a cylindrical roller at point
A
that prevents motion in the
x
and
´
directions. Use
the method of joints to determine the force supported
by member DG if PD40 kN and QD0kN.
Problem 6.72
The truss shown has a socket support at point
L
, a
roller at point
K
, and a cylindrical roller at point
A
that prevents motion in the
x
and
´
directions. Use
the method of joints to determine the force supported
by member MJ if PDQD10 kN.
Problem 6.73
The truss shown has a socket support at point
L
, a
roller at point
K
, and a cylindrical roller at point
A
that prevents motion in the
x
and
´
directions.
Use the method of sections to determine the force
supported by member
J G
if
PD40 kN
and
QD
0kN.
Problem 6.74
The truss shown has a socket support at point
L
, a
roller at point
K
, and a cylindrical roller at point
A
that prevents motion in the
x
and
´
directions.
Use the method of sections to determine the force
supported by member J G if PDQD10 kN.
Problem 6.75
A cork puller for removing the cork from a bottle is shown. Draw FBDs for all
of the members of the cork puller and the cork (i.e., members
AB
,
CD
,
LM
,
HBEDI
, and
JKL
), labeling all unknowns. Neglect the weights of members.
Problem 6.76
The keyboard mechanism for a piano consists of a large number of parts,
but for purposes of modeling the transmission of force and motion from
the key to the piano wire, the model shown can be used. Draw FBDs for all
of the members (i.e., members
ABC
,
DCE
,
EF
, and
GFH
), labeling all
unknowns. Neglect the weights of members.
Problem 6.77
A frame used for a chair is shown. Determine the force supported by members
ABCD,ECF G, and BF . Neglect friction at points Aand G.
Problem 6.78
A frame used for supporting a weight
WD800
N is shown. Determine the
force supported by cable DH and members ABCD,CEF G, and BE.
0:5.0:3 m/800 N.0:7 m/D0)TBE D 2333 N, (4)
XFxD0W CxTBE
0:3
Problem 6.79
The tool shown is used for picking up items that otherwise would be out of
a person’s reach. In the position shown, the torsional spring at
C
supports
a moment of
10 in:lb
, which tends to open the jaws of the tool. Neglect
the weights of the individual members and neglect friction at points
H
and
G
. Determine the forces supported by all members of the tool and the
force applied by the tool to the item being gripped at Hand G.
Problem 6.80
Compare the designs for the pickup tools shown in Fig. P6.79 and in Fig. 6.29 on p. 410. If the dimensions
of the members in these tools are approximately the same, speculate on which of these tools will be capable
of applying the greater force to the item being gripped at
H
and
G
before one of the members of the tool
fails. Note: Concept problems are about explanations, not computations.
Problem 6.81
The elevation and tilt angle of table AB are controlled by an operator’s hand at
point
D
. The table supports a box weighing
10 lb
with center of gravity at point
G
. Determine the force the operator must apply to keep the table in equilibrium,
and determine the force supported by all members of the machine. The force
applied by the operator is vertical.
Problem 6.82
The elevation and tilt angle of table AB are controlled by an operator’s hand at
point
D
. The table supports a box weighing
10 lb
with center of gravity at point
G
. Determine the force the operator must apply to keep the table in equilibrium,
and determine the force supported by all members of the machine. The force
applied by the operator is horizontal.
Problem 6.83
The elevation and tilt angle of table
AB
are controlled by an operator’s hand at
point
D
. The table supports a box weighing
40
N with center of gravity at point
G
. Determine the force the operator must apply to keep the table in equilibrium,
and determine the force supported by all members of the machine. The force
applied by the operator is vertical.
Problem 6.84
The elevation and tilt angle of table
AB
are controlled by an operator’s hand at
point
D
. The table supports a box weighing
40
N with center of gravity at point
G
. Determine the force the operator must apply to keep the table in equilibrium,
and determine the force supported by all members of the machine. The force
applied by the operator is horizontal.
Problem 6.85
For the ladder shown, if
WD800
N and
hD0:3
m, determine the force
supported by each of the spreader bars
BG
and
DG
. Neglect the weight of the
ladder and friction at points Aand E.