Hwk2B - is quickly dropped into an insulating Styrofoam...

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PHYS 153 Homework 2B Problem 1 (a) If an area measured on the surface of a solid body is A 0 at some initial temperature and then changes by Δ A when the temperature changes by Δ T , show that Δ A = (2 α ) A 0 Δ T , where α is the coefficient of linear expansion. (b) A circular sheet of aluminum is 55 . 0 cm in diameter at 15 . 0 C. By how much does the area of one side of the sheet change when the temperature increases to 27 . 5 C? Problem 2 (a) A wire that is 1 . 50 m long at 20 . 0 C is found to increase in length by 1 . 90 cm when warmed to 420 . 0 C. Compute its average coefficient of linear expansion for this temperature range. (b) The wire is stretched just taut (zero tension) at 420 C. Find the stress in the wire if it is cooled to 20 . 0 C without being allowed to contract. Young’s modulus for the wire is 2 . 0 × 10 11 Pa. Problem 3 A 500 . 0 g chunk of an unknown metal, which has been in boiling water for several minutes,
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Unformatted text preview: is quickly dropped into an insulating Styrofoam beaker containing 1 . 00 kg of water at room temperature (20 . C). After waiting and gently stirring for 5 . 00 minutes, you observe that the waters temperature has reached a constant value of 22 . C. (a) Assuming that the styrofoam absorbs a negligibly small amount of heat and that no heat was lost to the surroundings, what is the specic heat of the metal? (b) Which is more useful for storing thermal energy: this metal or an equal weight of water? Explain. (c) What if the heat absorbed by the Styrofoam actually is not negligible. How would the specic heat you calculated in part (a) be in error? Would it be too large, too small, or still correct? Explain. 1 - 1...
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