Chapter 9: Q9-2Q (page 230)
A bungee jumper momentarily comes to rest at the bottom of the dive before he springs back upward. At that moment, is the bungee jumper in equilibrium? Explain.
Yes, the bungee jumper is in equilibrium.
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(I) Approximately what magnitude force, \({F_{\bf{M}}}\)must the extensor muscle in the upper arm exert on the lower arm to hold a 7.3-kg shot put (Fig. 9–71)? Assume the lower arm has a mass of 2.3 kg and its CG is 12.0 cm from the elbow-joint pivot.
A steel rod of radius\(R = 15\;{\rm{cm}}\)and length\({l_0}\)stands upright on a firm surface. A 65-kg man climbs atop the rod. (a) Determine the percent decrease in the rod’s length. (b) When a metal is compressed, each atom moves closer to its neighboring atom by exactly the same fractional amount. If iron atoms in steel are normally\(2.0 \times {10^{ - 10}}\;{\rm{m}}\)apart, by what distance did this interatomic spacing have to change in order to produce the normal force required to support the man? [Note: Neighboring atoms repel each other, and this repulsion accounts for the observed normal force.
(II) A 15-cm-long tendon was found to stretch 3.7 mm by a force of 13.4 N. The tendon was approximately round with an average diameter of 8.5 mm. Calculate Young’s modulus of this tendon.
How close to the edge of the 24.0 kg table shown in Fig. 9–54 can a 66.0 kg person sit without tipping it over?
A uniform beam is hinged at one end and held in a horizontal position by a cable, as shown in Fig. 9–42. The tension in the cable
(a) must be at least half the weight of the beam, irrespective of the angle of the cable.
(b) could be less than half the beam’s weight for some angles.
(c) will be half the beam’s weight for all angles.
(d) will be equal to the beam’s weight for all angles.
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