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karna (pk4534) – 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. The electrons attract each other. 2. They cause a jam when they try to fly away. 3. They are attracted to the five thou- sand billion positively charged protons in the atomic nuclei of atoms in the penny. correct 4. The shell of the penny prevents the elec- trons from flying. 5. They don’t have enough speed. Explanation: The electrons are bound to the nuclei. 002 10.0 points How can a charged atom (an ion) attract a neutral atom? 1. The charged atom can produce secondary electrons to interact with the neutral atom and make it positively charged or negatively charged. 2. 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 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 41 g and charge 62 μ C is released from rest when it is 18 cm from a second particle of charge 20 μ C. Determine the magnitude of the initial ac- celeration of the 41 g particle. Correct answer: 8389 . 42 m / s 2 . Explanation: Let : m = 41 g , q = 62 μ C = 6 . 2 × 10 5 C , d = 18 cm = 0 . 18 m , Q = 20 μ C = 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 . 2 × 10 5 C vextendsingle vextendsingle vextendsingle vextendsingle 2 × 10 5 C vextendsingle vextendsingle (0 . 041 kg) (0 . 18 m 2 ) = 8389 . 42 m / s 2 . 004 10.0 points Two spheres, fastened to “pucks”, are rid- ing on a frictionless airtrack. Sphere “1” is charged with 2 nC, and sphere “2” is charged with 6 nC. Both objects have the same mass. 1 nC is equal to 1 × 10 9 C. As they repel, 1. they have the same magnitude of acceler- ation. correct 2. they do not accelerate at all, but rather separate at constant velocity.
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karna (pk4534) – HW01 – li – (59050) 2 3. sphere “2” accelerates 3 times as fast as sphere “1”. 4. sphere “1” accelerates 9 times as fast as sphere “2”. 5. sphere “1” accelerates 3 times as fast as sphere “2”.
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