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Unformatted text preview: zapata (jz883) HW #1 Antoniewicz (56495) 1 This printout should have 23 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points A particle of mass 63 g and charge 46 C is released from rest when it is 78 cm from a second particle of charge 18 C. Determine the magnitude of the initial ac celeration of the 63 g particle. Correct answer: 194 . 151 m / s 2 . Explanation: Let : m = 63 g , q = 46 C = 4 . 6 10 5 C , d = 78 cm = 0 . 78 m , Q = 18 C = 1 . 8 10 5 C , and k e = 8 . 9875 10 9 . The force exerted on the particle is F = k e  q 1  q 2  r 2 = ma bardbl vectora bardbl = k e bardbl vectorq bardblbardbl vector Q bardbl md 2 = k e vextendsingle vextendsingle 4 . 6 10 5 C vextendsingle vextendsingle vextendsingle vextendsingle 1 . 8 10 5 C vextendsingle vextendsingle (0 . 063 kg) (0 . 78 m 2 ) = 194 . 151 m / s 2 . 002 10.0 points Two small silver spheres, each with a mass of 75 g, are separated by 0 . 92 m. The num ber of electrons per atom of silver is 47, and the number of atoms per gram is Avogadros number divided by the molar mass of silver, 107 . 87 g / mol. Calculate the fraction of the electrons in one sphere that must be transferred to the other in order to produce an attrac tive force of 10000 N (about a ton) be tween the spheres. The Coulomb constant is 8 . 98755 10 9 N m 2 / C 2 and the Avogadros number is 6 . 02214 10 23 mol 1 . Correct answer: 3 . 07785 10 10 . Explanation: Let : m = 75 g , r = 0 . 92 m , n Ag = 47 , M Ag = 107 . 87 g / mol , f = 10000 N , and k e = 8 . 98755 10 9 N m 2 / C 2 . The force between the spheres is F = k e q 2 r 2 q = r radicalbigg F k e . The total charge is q = nq e n transferred = q q e = r q e radicalbigg F k e = . 92 m 1 . 60218 10 19 C radicalBigg 10000 N 8 . 98755 10 9 N m 2 / C 2 = 6 . 05699 10 15 where q e is the charge of one electron. There are n atoms = m M Ag N A atoms in each sphere, where N A is Avogadros number, so the total number of electrons is n electrons = n Ag n atoms = n Ag mN A M Ag = 47(75 g) 107 . 87 g / mol (6 . 02214 10 23 mol 1 ) = 1 . 96793 10 25 . Thus the ratio is R = n transferred n electrons = 6 . 05699 10 15 1 . 96793 10 25 = 3 . 07785 10 10 . zapata (jz883) HW #1 Antoniewicz (56495) 2 The fraction of electrons needed to create a significant force is very tiny. When we talk about the charge of macro scopic objects (like the silver spheres in this problem), we generally mean the surplus charge, which corresponds to only a tiny frac tion of the total number of electrons in the material....
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 Spring '10
 ANTONIEWICZ
 Physics, Charge, Mass

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