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Ch4 HW2 S2008

# Ch4 HW2 S2008 - Ch4 HW2 S2008 10:27 AM Web Assign Ch4 HW2...

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4/25/08 10:27 AM Ch4 HW2 S2008 Page 1 of 7 http://www.webassign.net/[email protected]/[email protected] Ch4 HW2 S2008 (Homework) KRISTIN SEILOFF PHYS 2211 M & N Spring 08, section N05, Spring 2008 Instructor: Jennifer Curtis Description Ball-spring model of a solid; tension forces; length of interatomic bond. Instructions Reading: Sec. 4.1-4.4 Web Assign Current Score: 51 out of 58 Due: Friday, February 8, 200812:00 PM EST 1. 6/6 points | 2/4 submissions A climber whose mass is 52 kg hangs motionless from a rope. What is the tension in the rope? tension = 509.6 510 N Later, a different climber whose mass is 78 kg hangs from the same rope. Now what is the tension in the rope? tension = 764.4 764 N Compare the physical state of the rope when it supports the heavier climber to the state of the rope when it supports the lighter climber. Which statements about the physical state of the rope are true? Check all that apply. [x] [x] The rope is slightly longer when it supports the heavier climber than when it supports the lighter climber. [x] [x] The interatomic bonds in the rope are stretched more when the rope supports the haevier climber than when the rope supports the lighter climber. [_] [_] Because the same rope is used, the tension in the rope must be the same in both cases. 2. 3/3 points | 2/4 submissions Why are two balls connected by a spring a good model for two atoms connected by a chemical bond? [x] [x] If the two atoms get closer together than the equilibrium interatomic distance, they repel each other. [x] [x] The magnitude of the force one atom exerts on another is proportional to the stretch or compression of the bond between them. [_] [_] Each spring represents a real microscopic coiled metal wire that connects two adjacent atoms. [x] [x] If the two atoms get farther apart than the equilibrium interatomic distance, they attract each other. 3. 2/2 points | 1/4 submissions

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4/25/08 10:27 AM Ch4 HW2 S2008 Page 2 of 7 http://www.webassign.net/[email protected]/[email protected] Consider a 4 kg block of magnesium modeled as an array of balls connected by springs, as shown in Figure 4.6 on page 107. What is the mass in kg of a single "ball" in the ball-spring model? One mole (6.02 10 23 atoms) of magnesium has a mass of 24 grams, as shown in the periodic table on the inside front cover of the textbook. (_) (_) 0.024 kg (_) (_) 6.02 10 23 kg (_) (_) 4 kg (o) (o) 3.99 10 -26 kg (_) (_) 166.7 kg (_) (_) 6.64 10 -24 kg 4. 6/6 points | 3/4 submissions The diameter of a copper atom is approximately 2.28e-10 m. The mass of one mole of copper is 64 grams. Assume that the atoms are arranged in a simple cubic array, as shown in Figure 4.10, on p. 109. Remember to convert to S.I. units.
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