Page 262 - Fisika Terapan for Engineers and Scientists

462 CHAPTER 14 Statics and Elasticity

REVIEW PROBLEMS

89. A traffic lamp of mass 25 kg hangs from a wire stretched
between two posts. The traffic lamp hangs at the middle of
the wire, and the two halves of the wire sag downward at an
angle of 20 (see Fig. 14.67). What is the tension in the wire?
Assume the wire is massless. 60°

20° 30°

25 kg

FIGURE 14.67 A traffic lamp.
FIGURE 14.69 Cargo hanging from a boom.

90. A heavy shop sign hangs from a boom sticking out horizon-
tally from a building (see Fig. 14.68). The boom is hinged at
the building and is supported by a diagonal wire, making an
angle of 45 with the boom. The mass of the sign is 50 kg,
and the boom and the wire are massless. What is the tension
in the wire? What is the force with which the end of the
boom pushes against the building? 8000 N

FIGURE 14.70 Tractor pulling trailer.

45°

the torque exerted by the axle on the wheel, but neglect the
weight of the wheel. If the tractor is to provide a pull of 8000
N (a pull of 4000 N from each rear wheel), what torque must
the axle exert on each rear wheel?
94. One end of a string is tied to a meterstick at the 80-cm mark,
and the other end is tied to a hook in the ceiling. You push
against the bottom edge of the meterstick at the 30-cm mark,
FIGURE 14.68 Sign hanging from a boom. so the stick is held horizontally (see Fig. 14.71). The mass of
the meterstick is 0.24 kg. What is the magnitude of the force
you must exert? What is the tension in the string?
91. Figure 14.69 shows cargo hanging from the loading boom of
a ship. If the boom is inclined at an angle of 30 and the cargo
has a mass of 2500 kg, what is the tension in the upper cable?
What is the compressional force in the boom? Neglect the
mass of the boom.
92. Repeat the calculation of Problem 91, but assume that the
mass of the boom is 800 kg, and that this mass is uniformly
distributed along the length of the boom.
93. A tractor pulls a trailer along a street (see Fig. 14.70). The
rear wheels, which are connected to the engine by means of
the axle, have a radius of 0.60 m. Draw a “free-body” diagram
for one of the rear wheels; be sure to include the forces and FIGURE 14.71 Meterstick tied to a hook.