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# solution1_pdf - white (rw22679) – Hw01 – Ross –...

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Unformatted text preview: white (rw22679) – Hw01 – Ross – (10219) 1 This print-out should have 16 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points You have 2 . 8 kg of water. One mole of water has a mass of 17 . 9 g / mol and each molecule of water contains 10 electrons since water is H 2 O. What is the total electron charge contained in this volume of water? Correct answer: − 1 . 50722 × 10 8 C. Explanation: Let : N A = 6 . 02214 × 10 23 molec / mol , q e = − 1 . 6 × 10 − 19 C / electron , m = 2 . 8 kg , M = 17 . 9 g / mol = 0 . 0179 kg / mol , and Z = 10 electrons / molec . The mass is proportional to the number of molecules, so for m grams in n molecules and M grams in N A molecules, m M = n N A n = m M N A Since 10 electrons are in each molecule of water, then the total number of electrons n e in the coin is n e = Z n = Z m M N A and the total charge q for the n e electrons is q = n e q e = Z m N A q e M = (10 electrons / molec) 2 . 8 kg . 0179 kg / mol × ( 6 . 02214 × 10 23 molec / mol ) × ( − 1 . 6 × 10 − 19 C / electron ) = − 1 . 50722 × 10 8 C . 002 (part 1 of 2) 10.0 points Three charges are arranged in a triangle as shown. + − + . 193 m . 888 m 6 . 17 nC − 2 . 8 nC 2 . 8 nC y x What is the net electrostatic force on the charge at the origin? The Coulomb constant is 8 . 98755 × 10 9 N · m 2 / C 2 . Correct answer: 4 . 17305 × 10 − 6 N. Explanation: Let : q 1 = 6 . 17 nC = 6 . 17 × 10 − 9 C , q 2 = 2 . 8 nC = 2 . 8 × 10 − 9 C , q 3 = − 2 . 8 nC = − 2 . 8 × 10 − 9 C , r 1 , 2 = 0 . 888 m , r 1 , 3 = 0 . 193 m , and k C = 8 . 98755 × 10 9 N · m 2 / C 2 . F 1 , 2 F 1 , 3 F θ The repulsive force F 1 , 2 = k C q 1 q 2 r 2 1 , 2 = 8 . 98755 × 10 9 N · m 2 / C 2 × ( 6 . 17 × 10 − 9 C )( 2 . 8 × 10 − 9 C ) (0 . 888 m) 2 = 1 . 96906 × 10 − 7 N white (rw22679) – Hw01 – Ross – (10219) 2 acts along the negative x-axis, and the attrac- tive force F 1 , 3 = k C q 1 | q 3 | r 2 1 , 3 = 8 . 98755 × 10 9 N · m 2 / C 2 × ( 6 . 17 × 10 − 9 C )( − 2 . 8 × 10 − 9 C ) (0 . 193 m) 2 = − 4 . 1684 × 10 − 6 N acts along the negative y-axis. Thus F net = bracketleftbig (1 . 96906 × 10 − 7 N) 2 +( − 4 . 1684 × 10 − 6 N) 2 bracketrightbig 1 / 2 = 4 . 17305 × 10 − 6 N . 003 (part 2 of 2) 10.0 points What is the direction of this force (as an angle between − 180 ◦ and 180 ◦ measured from the positive x-axis, with counterclockwise posi- tive)? Correct answer: − 92 . 7045 ◦ ....
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## This note was uploaded on 12/01/2010 for the course PHYSICS 21900 taught by Professor Rhoads during the Spring '10 term at IUPUI.

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solution1_pdf - white (rw22679) – Hw01 – Ross –...

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