Page 157 - Schaum's Outline of Theory and Problems of Applied Physics

142 EQUILIBRIUM [CHAP. 11

11.7. A 5-1b picture is held up by two strings that go from its upper corners to a hook on the wall. Each string has a
breaking strength of 3 lb. The maximum angle between the strings if they are not to break is

(a) 34 ◦ (c) 56 ◦
(b) 67 ◦ (d) 80 ◦

11.8. A picture hangs from two wires that go from its upper corners to a nail in the wall. If the picture weighs 8.0 N and
each wire makes a 30 angle with the vertical, the tension in each wire is
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(a) 4.0 N (c) 8.0 N
(b) 4.6 N (d) 9.2 N

11.9. An 0.80-kN load hangs from the end of a horizontal boom 2.0 m long hinged to a vertical mast. A rope 2.5 m long
joins the end of the boom with a point on the mast 1.5 m above the hinge. The tension in the rope is
(a) 0.48 kN (c) 1.00 kN
(b) 0.80 kN (d) 1.33 kN

11.10. The boom of Question 11.9 exerts an inward force on the hinge of
(a) 0.60 kN (c) 1.07 kN
(b) 0.80 kN (d) 1.67 kN

11.11. A 50-kg barrel hangs from one end of a 30-kg beam 3.0 m long. The distance from the loaded end to the balance
point is
(a) 56 cm (c) 94 cm
(b) 75 cm (d) 113 cm

11.12. A 50-kg steel pipe 4.0 m long is supported by a rope attached 1.7 m from one end. The downward force that must
be applied to the end of the pipe closest to the rope to keep the pipe horizontal is

(a) 8.8 N (c) 227 N
(b) 86 N (d) 490 N

Supplementary Problems

11.1. A weight is suspended from the middle of a rope whose ends are at the same height. Is it possible for the tension in
the rope to be sufficiently great to prevent the rope from sagging at all?
11.2. A couple consists of two equal forces that act along parallel lines of action in opposite directions. If each of the
forces in a couple has the magnitude F and their lines of action are d apart, find the torque exerted by the couple.
11.3. The wheels of a certain bus are 2 m apart, and the bus falls over when it is tilted sideways at a 45 angle. How high
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above the road is the center of gravity of the bus?

11.4. A 40-N box is suspended from two ropes which each make a 45 angle with the vertical. What is the tension in each
◦
rope?
◦
11.5. A 100-kg box is suspended from two ropes; the left one makes an angle of 20 with the vertical, and the other makes
an angle of 40 . What is the tension in each rope?
◦
11.6. A load of unknown weight is suspended from the end of a horizontal boom whose own weight is negligible. The
angle between the boom and the cable supporting its end is 30 , and the tension in the cable is 400 N. Find the
◦
weight of the load.