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PROBLEM 12.19 (Continued)
PROBLEM 12.19 (Continued)
PROBLEM 12.20
The flat-bed trailer carries two 1500-kg beams with the upper
beam secured by a cable. The coefficients of static friction
between the two beams and between the lower beam and the
bed of the trailer are 0.25 and 0.30, respectively. Knowing that
the load does not shift, determine (a) the maximum acceleration
of the trailer and the corresponding tension in the cable, (b) the
maximum deceleration of the trailer.
:0.25Fma mgma
2
0.25 2.45 m/sag
PROBLEM 12.20 (Continued)
2 : 0.30 2 2Fma mg ma
2
0.30 2.94 m/sag
The smaller of deceleration value of Case 1 governs. 2
2.45 m/sa
PROBLEM 12.21
A baggage conveyor is used to unload luggage from an airplane.
The 10-kg duffel bag A is sitting on top of the 20-kg suitcase B.
The conveyor is moving the bags down at a constant speed of
0.5 m/s when the belt suddenly stops. Knowing that the
coefficient of friction between the belt and B is 0.3 and that bag A
does not slip on suitcase B, determine the smallest allowable
coefficient of static friction between the bags.
PROBLEM 12.21 (Continued)
PROBLEM 12.22
To unload a bound stack of plywood from a truck, the driver first tilts the
bed of the truck and then accelerates from rest. Knowing that the
coefficients of friction between the bottom sheet of plywood and the bed
are 0.40
s
and 0.30,
k
determine (a) the smallest acceleration of
the truck which will cause the stack of plywood to slide, (b) the
acceleration of the truck which causes corner A of the stack to reach the
end of the bed in 0.9 s.
PROBLEM 12.22 (Continued)
PROBLEM 12.23
To transport a series of bundles of shingles A
to a roof, a contractor uses a motor-driven lift
consisting of a horizontal platform BC which
rides on rails attached to the sides of a ladder.
The lift starts from rest and initially moves
with a constant acceleration
a
1
as shown. The
lift then decelerates at a constant rate
a
2
and
comes to rest at D, near the top of the ladder.
Knowing that the coefficient of static friction
between a bundle of shingles and the
horizontal platform is 0.30, determine the
largest allowable acceleration
a
1
and the
largest allowable deceleration
a
2
if the bundle
is not to slide on the platform.
PROBLEM 12.23 (Continued)
