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Unformatted text preview: Patel (sap785) homework #5 shubeita (58645) 1 This printout should have 16 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points Normally the rate at which you expend energy during a brisk walk is 3 . 5 calories per minute. (A calorie is the common unit of food energy, equal to 0 . 239 Joules.) How long do you have to walk in order to produce the same amount of energy as in a candy bar (approximately 280 cal)? Correct answer: 80 min. Explanation: Let : P = 3 . 5 cal / min and E = 280 cal . t = E P = 280 cal 3 . 5 cal / min = 80 min . 002 (part 1 of 3) 10.0 points The current theory of the structure of the Earth, called plate tectonics, tells us that the continents are in constant motion. Assume that the North American continent can be represented by a slab of rock 5150 km on a side and 32 km deep and that the rock has an average mass density of 2770 kg / m 3 . The continent is moving at the rate of about 3 . 8 cm / year. What is the mass of the continent? Correct answer: 2 . 35095 10 21 kg. Explanation: Let : = 5150 km , d = 32 km , and = 2770 kg / m 3 . m = V = 2 d = (5150 km) 2 (32 km) (2770 kg / m 3 ) parenleftbigg 1000 m km parenrightbigg 3 = 2 . 35095 10 21 kg . 003 (part 2 of 3) 10.0 points What is the kinetic energy of the continent? Correct answer: 1706 . 74 J. Explanation: Let : m = 2 . 35095 10 21 kg and v = 3 . 8 cm / year . v = (3 . 8 cm / year) m 100 cm y 365 d d 24 h h 3600 s = 1 . 20497 10 9 m / s , K = 1 2 mv 2 = 1 2 (2 . 35095 10 21 kg) (1 . 20497 10 9 m / s) 2 = 1706 . 74 J . 004 (part 3 of 3) 10.0 points A jogger (of mass 60 kg) has the same kinetic energy as that of the continent. What would his speed be? Correct answer: 7 . 54264 m / s. Explanation: For the jogger, Let : m jogger = 60 kg and K jogger = 1706 . 74 J . Patel (sap785) homework #5 shubeita (58645) 2 K = 1 2 mv 2 v jogger = radicalBigg 2 K m jogger = radicalBigg 2 (1706 . 74 J) 60 kg = 7 . 54264 m / s . 005 (part 1 of 2) 10.0 points A 1 . 01 10 3 kg car accelerates uniformly from rest to 13.8 m/s in 3.59 s. a) What is the work done on the car in this time interval? Correct answer: 96172 . 2 J. Explanation: Basic Concept: W net = KE = KE f KE i = 1 2 mv 2 f since v i = 0 m/s....
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This note was uploaded on 04/16/2010 for the course PHY 317k taught by Professor Kopp during the Spring '07 term at University of Texas at Austin.
 Spring '07
 KOPP

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