This week’s assignment has two questions on Fluids, and 4 on Ideal Gases. For fluids -- reading are same as past week; Now add the following for Ideal Gases. You will find that the way I will cover Thermodynamics is very different from that in Knight’s book. So keep up with the lecture and the lecture slides. The material is all there in the text, but I feel that it is not organized in a sensible way.

Problem 1: The wider and narrower segments of pipe have radii 6.0 cm and 2.0 cm, respectively.A pump steadily pushes water into the left end of the system. At the right end, the water shootsinto the air at 35.0 m/s.(a) Find the pressure supplied by the pump.(b) How many liters per second of water does the pump push into the left end of the system? Explain.(c) The system is rotated 90° so that water flows up instead of sideways. The pump supplies the samepressure as before. Does water now leave the thinner tube with a speed greater than, less than, orequal to 35.0 m/s? Explain qualitatively, with no formulas.(d) Now use Bernoulliʼs law to check your part (c) reasoning. Reconcile if needed.

Problem 2: The top surface of the water in a cup has area Atop = 25.0 cm2, while a hole in the bottom of the cup has area Ah = 2.50 cm2. The cup of height H = 18.0 cm is initially filled with water. Find the water’s speed as it exits the hole, before the water level in the cup has changed significantly. Answer symbolically, in terms of Atop, Ah, pair (air pressure), H, and constants, before substituting values. The question is difficult. If you like a challenge, try to solve this without the hint. Otherwise, look at http://ayush.pbworks.com/HW5-Hints

Problem 3: A box of total length 1.0 m and cross sectional area A has a partition inside that can slide freely left and right. There are N1 = 2.0 x 1023 gas atoms on the left side of the partition, and N2 = 3N1 = 6.0 x1023 atoms on the right side. The gas on both sides is at the same temperature T (the room temperature). The partition is initially held at center of the box, and is then released. After a short time, it settles into its final, equilibrium position.(a) After being released, does the partition moves to the right, to the left, or not at all. Explain your reasoning without doing calculations.(b) Answer without doing a detailed calculation: how far from the left end

of the box is the partition once it has settled?(c) Confirm your part (b) answer by calculating where the partition settles

using the ideal gas law and other physical laws as needed. (Assume that the box can conduct heat from outside.)

P4: Imagine that a cylinder with a piston were immersed in an ice water bath, as shown at right. After it has been sitting in the ice water bath for a while, it is moved to a boiling water bath and allowed to sit there for quite some time. (The piston-lid is free to move up and down, but it does not come off or leak.)(a) Compare the final pressure of the gas to the initial pressure. Explain your reasoning. (Hint:

Think about the forces on the lid)(b) Compare the final volume of the gas to the initial pressure. Explain your reasoning using (i)

kinetic theory and (ii) the ideal gas law.(c) Draw a PV diagram for the process. Explain. (Check your graph against with your answers in

parts above)

Phys260 HW 5 (Fluids and Ideal Gases)Due Thursday 10/15/09, start of lecture

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P5: At very high temperatures, chlorine gas molecules (Cl2) vibrate; the two chlorine atoms behave as if attached by a tiny spring. At low temperatures, the molecules don’t vibrate. It takes 50 J of energy to heat up a certain very cold sample of chlorine gas by 10° C. How much energy would it take to heat up that same amount of chlorine by 10° C when it is very hot to begin with? [Hints on webpage]

P6: A sealed test tube contains helium, the atoms of which bounce around with average speed (more precisely, root mean square speed) 1000 m/s. Enough energy is added to the helium so that the root mean square speed triples, to 3000 m/s. Two students discuss how the pressure in the tube changes: Leona: “Since they’re moving three times as fast, the atoms collide with the walls of the test tube three times as often, which triples the pressure.” Kimberly: “I agree that the pressure triples, but I think it’s for a different reason. Since the atoms are moving three times as fast, they hit the walls of the test tube three times as hard, and that’s why the pressure triples.”(a) In what ways do you agree and disagree with Leona’s idea?(b) In what ways do you agree and disagree with Kimberly’s idea?(c) Does the pressure triple, or does it increase by some other factor? Explain.

Phys260 HW 5 (Fluids and Ideal Gases)Due Thursday 10/15/09, start of lecture