HW_1_sol2

# HW_1_sol2 - P112 Spring 2007 Homework#1 Solutions(of boxed...

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P112 Spring 2007 Homework #1 Solutions (of boxed problems only) 1. Total distance is 20 miles, total time is 1.5 h. Average speed is 20/1.5 = 13.3 miles per hour. 2. 1 km = 1000 m and 1 hr = 3600 s, therefore 1228.0 km/h = 341.1 m/s. That’s faster than the speed of sound! 4. a. First let’s convert to km/L. 21 mi/gal = 21*1.6 km/3.8 L = 8.8 km/L. If the car goes 8.8 km with every liter of fuel, it will take 100/8.8 = 11.4 L/100km. b. 6 L/100km = 2.5 gal/100mi. That’s 40 mi/gal. 5. (a) The times spent going up and down the hill are: t 1 = D/v 1 and t 2 = D/v 2 The total time is: t 1 + t 2 = D/v 1 + D/v 2 The average velocity is the total distance 2D divided by the total time: v av = 2D/( D/v 1 + D/v 2 ) = 2v 1 v 2 v 1 + v 2 As long as the distance is the same for going up and down the average velocity does not depend on D. (b) v av = 2v 1 2 /(2v 1 ) = v 1 . This makes sense because the average velocity is the same as the (constant) instantaneous velocity. (c) v av 2v 1 v 2 /(v 2 ) = 2v 1 . This also makes sense. Since the time to cover the second distance D is

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• Spring '08
• Wheeler
• Work, North Pole, 21 mi, 100mi, 11.4 L, 6.0 mi

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