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PROBLEM 8.136 (Continued)
PROBLEM 8.137
A slender rod of length L is lodged between peg C and the vertical wall and
supports a load P at end A. Knowing that the coefficient of static friction
between the peg and the rod is 0.15 and neglecting friction at the roller,
determine the range of values of the ratio L/a for which equilibrium is
maintained.
PROBLEM 8.138
The hydraulic cylinder shown exerts a force of 3 kN directed
to the right on Point B and to the left on Point E. Determine
the magnitude of the couple M required to rotate the drum
clockwise at a constant speed.
PROBLEM 8.139
A rod DE and a small cylinder are placed between two guides as shown. The
rod is not to slip downward, however large the force P may be; i.e., the
arrangement is said to be self-locking. Neglecting the weight of the cylinder,
determine the minimum allowable coefficients of static friction at A, B, and C.
PROBLEM 8.140
Bar AB is attached to collars that can slide on the inclined rods
shown. A force P is applied at Point D located at a distance a from
end A. Knowing that the coefficient of static friction
s
between
each collar and the rod upon which it slides is 0.30 and neglecting
the weights of the bar and of the collars, determine the smallest
value of the ratio a/L for which equilibrium is maintained.
PROBLEM 8.141
Two 10 wedges of negligible weight are used to move and position the 400-
lb block. Knowing that the coefficient of static friction is 0.25 at all surfaces
of contact, determine the smallest force P that should be applied as shown to
one of the wedges.
PROBLEM 8.142
A 10 wedge is used to split a section of a log. The coefficient of static
friction between the wedge and the log is 0.35. Knowing that a force P of
magnitude 600 lb was required to insert the wedge, determine the magnitude
of the forces exerted on the wood by the wedge after insertion.
PROBLEM 8.143
In the gear-pulling assembly shown the square-threaded screw AB has a mean radius
of 15 mm and a lead of 4 mm. Knowing that the coefficient of static friction is 0.10,
determine the couple that must be applied to the screw in order to produce a force of
3 kN on the gear. Neglect friction at end A of the screw.
PROBLEM 8.144
A lever of negligible weight is loosely fitted onto a 30-mm-
radius fixed shaft as shown. Knowing that a force P of
magnitude 275 N will just start the lever rotating clockwise,
determine (a) the coefficient of static friction between the
shaft and the lever, (b) the smallest force P for which the
lever does not start rotating counterclockwise.
PROBLEM 8.145
In the pivoted motor mount shown the weight W of the 175-
lb motor is used to maintain tension in the drive belt.
Knowing that the coefficient of static friction between the
flat belt and drums A and B is 0.40, and neglecting the
weight of platform CD, determine the largest couple that can
be transmitted to drum B when the drive drum A is rotating
clockwise.
