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PROBLEM 8.33
A pipe of diameter 60 mm is gripped by the stillson wrench shown. Portions
AB and DE of the wrench are rigidly attached to each other, and portion CF is
connected by a pin at D. If the wrench is to grip the pipe and be self-locking,
determine the required minimum coefficients of friction at A and C.
PROBLEM 8.34
A safety device used by workers climbing ladders fixed to high
structures consists of a rail attached to the ladder and a sleeve that can
slide on the flange of the rail. A chain connects the worker’s belt to
the end of an eccentric cam that can be rotated about an axle attached
to the sleeve at C. Determine the smallest allowable common value of
the coefficient of static friction between the flange of the rail, the pins
at A and B, and the eccentric cam if the sleeve is not to slide down
when the chain is pulled vertically downward.
PROBLEM 8.34 (Continued)
PROBLEM 8.35
To be of practical use, the safety sleeve described in Problem 8.34
must be free to slide along the rail when pulled upward. Determine
the largest allowable value of the coefficient of static friction
between the flange of the rail and the pins at A and B if the sleeve is
to be free to slide when pulled as shown in the figure, assuming
(a)
60 ,
(b)
50 ,
(c)
40 .
PROBLEM 8.35 (Continued)
PROBLEM 8.36
Two 10-lb blocks A and B are connected by a slender rod of negligible weight. The
coefficient of static friction is 0.30 between all surfaces of contact, and the rod
forms an angle
30 .
with the vertical. (a) Show that the system is in
equilibrium when
0.P
(b) Determine the largest value of P for which
equilibrium is maintained.
PROBLEM 8.37
A 1.2-m plank with a mass of 3 kg rests on two joists. Knowing
that the coefficient of static friction between the plank and the
joists is 0.30, determine the magnitude of the horizontal force
required to move the plank when (a) a = 750 mm, (b) a = 900 mm.
PROBLEM 8.37 (Continued)
PROBLEM 8.38
Two identical uniform boards, each of weight 40 lb, are temporarily
leaned against each other as shown. Knowing that the coefficient of
static friction between all surfaces is 0.40, determine (a) the largest
magnitude of the force
P
for which equilibrium will be maintained,
(b) the surface at which motion will impend.
11.429 lb
PROBLEM 8.38 (Continued)
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