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solution1_pdf - welker(lmw523 HW01 li(59050 This print-out...

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welker (lmw523) – HW01 – li – (59050) 1 This print-out should have 23 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points The five thousand billion freely moving elec- trons in a penny repel one another. Why don’t they fly off the penny? 1. They are attracted to the five thou- sand billion positively charged protons in the atomic nuclei of atoms in the penny. correct 2. They don’t have enough speed. 3. They cause a jam when they try to fly away. 4. The shell of the penny prevents the elec- trons from flying. 5. The electrons attract each other. Explanation: The electrons are bound to the nuclei. 002 10.0 points How can a charged atom (an ion) attract a neutral atom? 1. An ion polarizes a nearby neutral atom, so that the part of the atom nearer to the ion acquires a charge opposite to the charge of the ion, and the part of the atom farther from the ion acquires a charge of the same sign as the ion. correct 2. The charged atom can produce secondary electrons to interact with the neutral atom and make it positively charged or negatively charged. 3. The charged atom can emit x rays to induce ionization of the neutral atom. 4. The charged atom can hit the neutral atom and make it positively charged or nega- tively charged. Explanation: An ion polarizes a nearby neutral atom, so that the part of the atom nearer to the ion acquires a charge opposite to the charge of the ion, and the part of the atom farther from the ion acquires a charge of the same sign as the ion. 003 10.0 points A particle of mass 40 g and charge 63 μ C is released from rest when it is 67 cm from a second particle of charge 12 μ C. Determine the magnitude of the initial ac- celeration of the 40 g particle. Correct answer: 378 . 4 m / s 2 . Explanation: Let : m = 40 g , q = 63 μ C = 6 . 3 × 10 5 C , d = 67 cm = 0 . 67 m , Q = 12 μ C = 1 . 2 × 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 = m a bardbl vectora bardbl = k e bardbl vectorq bardbl bardbl vector Q bardbl m d 2 = k e vextendsingle vextendsingle 6 . 3 × 10 5 C vextendsingle vextendsingle vextendsingle vextendsingle 1 . 2 × 10 5 C vextendsingle vextendsingle (0 . 04 kg) (0 . 67 m 2 ) = 378 . 4 m / s 2 . 004 10.0 points Two spheres, fastened to “pucks”, are rid- ing on a frictionless airtrack. Sphere “1” is charged with 1 nC, and sphere “2” is charged with 5 nC. Both objects have the same mass. 1 nC is equal to 1 × 10 9 C. As they repel, 1. sphere “1” accelerates 25 times as fast as sphere “2”. 2. they do not accelerate at all, but rather separate at constant velocity.
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welker (lmw523) – HW01 – li – (59050) 2 3. sphere “1” accelerates 5 times as fast as sphere “2”. 4. sphere “2” accelerates 5 times as fast as sphere “1”.
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