Page 158 - Schaum's Outline of Theory and Problems of Applied Physics

CHAP. 11] EQUILIBRIUM 143

11.7. A 2000-N steel beam is raised by a crane, and a horizontal rope is used to pull it into position in a bridge under
construction. What is the tension in the rope when the supporting cable is at an angle of 15 from the vertical?
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11.8. A 1-kg pigeon sits on the middle of a clothesline whose supports are 10 m apart. The clothesline sags by 1 m. If the
weight of the clothesline is negligible, find the tension in it.

11.9. A 30-lb weight is attached to one end of a 6-ft uniform beam whose own weight is 20 lb. Where is the balance point
of the system?
11.10. A pail of water is to be carried by a man and a boy who each hold one end of a 180-cm pole thrust through the pail’s
handle. Where should the pail be located along the pole so that the man carries twice as much weight as the boy?
Neglect the pole’s weight.

11.11. A 20-kg child and a 30-kg child sit at opposite ends of a 4-m seesaw that is pivoted at its center. Where should
another 20-kg child sit in order to balance the seesaw?

11.12. The axles of a 2400-lb car are 7 ft apart. If the center of gravity of the car is 3 ft behind the front axle, how much
weight is supported by each of the car’s wheels?

11.13. (a) A 50-kg horizontal boom 4 m long is hinged to a vertical mast, and its outer end is supported by a cable attached
to the mast 3 m above the hinge pin. Find the tension in the cable. (b) A load of 200 kg is suspended from the outer
end of the boom. Find the new tension in the cable.
11.14. Solve Prob. 11.13 by considering the rotational equilibrium of the boom, using the lower end of the boom as the
pivot point.

11.15. A door 7 ft high and 3 ft wide has hinges at the top and bottom of one edge. Half the 40-lb weight of the door is
supported by each hinge. Find the horizontal components of the force the door exerts on each hinge.

11.16. A 10-kg ladder 2.5 m long rests against a frictionless wall with its base on the floor 80 cm from the wall. How much
force does the top of the ladder exerts on the wall?

11.17. A 15-kg ladder 3 m long rests against a frictionless wall at a point 2.4 m from the ground. Find the vertical and
horizontal components of the force that the ladder exerts on the floor.

11.18. A steel pipe 2 m long has another steel pipe of the same kind 1 m long welded across one end, so the result has the
form of a T. Where is the center of gravity of this object located?

Answers to Multiple-Choice Questions

11.1. (b), (c) 11.7. (b)

11.2. (c) 11.8. (b)
11.3. (c) 11.9. (d)

11.4. (d) 11.10. (c)

11.5. (a) 11.11. (a)

11.6. (c) 11.12. (b)