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Unformatted text preview: PHY302 K. Solutions for midterm test #1. Problem 1 : Given the weight of air over a unit area, P = 10 N / cm 2 , the net weight of the entire atmosphere is obviously W atm = P A E . (S . 1) All we need to do is to calculate the Earths surface area in square centimeters. So, lets convert the Earths radius R E to centimeters: R = 6380 km = 6 . 38 10 3 km = 6 . 38 10 6 m = 6 . 38 10 8 cm . Consequently, A E = 4 R 2 E = 4 (6 . 38 10 8 cm) 2 = 4 6 . 38 2 10 16 cm 2 = 511 10 16 cm 2 = 5 . 11 10 18 cm 2 and hence W atm = P A E = 10 N / cm 2 5 . 11 10 18 cm 2 = 5 . 11 10 19 N . (S . 2) Problem 2 : Consider the cars motion in 3 distinct stages: (1) Accelerating from zero to v f = 30 m/s. This stage takes time t 1 = 10 s, and the car moves through distance L 1 = 1 2 a 1 t 2 1 = t 2 1 2 parenleftbigg a 1 = v f t 1 parenrightbigg = t 1 v f 2 = 10 s 30 m / s 2 = 150 m . (S . 3) (2) Cruising at constant speed v = 30 m/s. During this stage the car moves through L 2 = 300 m, which takes time t 2 = L 2 /v = (300 m) / (30 m / s) = 10 s....
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This note was uploaded on 11/11/2010 for the course PHY 302K taught by Professor Kaplunovsky during the Spring '08 term at University of Texas at Austin.
 Spring '08
 Kaplunovsky

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