Hwk4A

# Hwk4A - A reference book on solar energy shows that the...

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PHYS 153 Homework 4A Problem 1 A 10 cm diameter, 20 cm long cylinder contains 2 . 0 × 10 22 atoms of argon at a temperature of 50 C. (a) What is the number density of the gas? (b) What is the root-mean-square speed? (c) What is ( v x ) rms , the rms value of the x -component of velocity? (d) Determine the pressure in the cylinder using the ideal-gas law. Problem 2 A 100 cm 2 box contains helium at a pressure of 2 . 0 atm and a temperature of 100 C. It is placed in thermal contact with a 200 cm 2 box containing argon at a pressure of 4 . 0 atm and a temperature of 400 C. (a) What is the initial thermal energy of each gas? (b) What is the ﬁnal thermal energy of each gas? (c) What is the ﬁnal temperature? Problem 3 A 10 m × 14 m house is built on a 12 cm thick concrete slab. What is the heat-loss rate through the slab if the ground temperature is 5 C while the interior of the house is 22 C? Problem 4 You would like to put a solar hot water system on your roof, but you’re not sure it’s feasible.
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Unformatted text preview: A reference book on solar energy shows that the ground-level solar intensity in your city is 800 W / m 2 for at least 5 hours a day throughout most of the year. Assuming that a completely black collector plate loses energy only by radiation, and that the air temperature is 20 ◦ C, what is the equilibrium temperature of a collector plate directly facing the sun? Note that while a plate has two sides, only the side facing the sun will radiate because the opposite side will be well insulated. Problem 5 A cubical box 20 cm on a side is constructed from 1 . 2 cm thick concrete panels. A 100 W lightbulb is sealed inside the box. What is the air temperature inside the box when the light is on if the surrounding air temperature is 20 ◦ C? 1 - 1...
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