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Unformatted text preview: ©2010 Sarah L. Keller Chem 452, Homework #2 • See syllabus for due dates. No late homework will be accepted on this or future homework sets. • Some students say that this is the hardest homework set all quarter, so get an early start and work together. Motto: Sometimes life gives you exactly the information you need… sometimes too little … sometimes too much. The trick is to figure out what you do need. (1) You are encouraged to work together on the homework. Meet at least four fellow students in the class that you have not met previously and write down their first and last names. (2 ) a) Fill in one or two steps to show that the integration indeed yields the answer shown. work spring = f spring ¡ ¢ dx = k spring ( x £ x ) ¢ dx x i x f ¡ = k spring 2 x f £ x ( ) 2 £ x i £ x ( ) 2 ¤ ¥ ¦ § b) Calculate the work in joules done for a system in which a muscle of 1 cm 2 cross section and 10.0 cm length is stretched to 11.0 cm by hanging a mass on it. The muscle behaves like a spring. The spring constant for the muscle was determined by finding that the muscle exerts a force of 5.00 N when it is stretched from 10.0 to 10.5cm. (This problem was taken from Tinoco Ch 2, Prob 3, part c.) (3) a) At sea level, the pressure that air exerts on your body is 1 atm. Consider a square piece of ground 1 m 2 . What is the mass of all of the air above this square? (Answer ¡ 1.03 x 10 4 kg.) b) Suppose you jump in Lake Washington, what is the difference in pressure you feel at the surface compared to at about 10 meters ( ¡ 30 feet) down? (Hint: for a liquid you can usually assume that density is almost constant with changes in pressure.) c) If the 1 st floor of Bagley Hall were at sea level, what would be the difference in pressure of the air on the 4 th floor compared to on the 1 st floor (3 stories ¡ 10 meters)? (This is the most challenging question on this set.) (Hint: for a gas, you cannot assume that either volume or density is constant with changes in pressure, but you may assume that air acts as an ideal gas, that its molecular weight is 0.029kg/mol, and that its temperature on the 1 st floor is the same as on the 4...
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 Winter '09
 robinson
 Energy, Sarah L. Keller

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