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Phys251 hw3

# Phys251 hw3 - lai(yl8859 HW03 gavrin(25111 This print-out...

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lai (yl8859) – HW03 – gavrin – (25111) 1 This print-out should have 10 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points A neutral ball is suspended by a string. A positively charged insulating rod is placed near the ball, which is observed to be at- tracted to the rod. Why is this? 1. The ball becomes positively charged by induction. 2. The number of electrons in the ball is greater than in the rod. 3. The ball becomes negatively charged by induction. 4. The string is not a perfect conductor. 5. There is a rearrangement of the electrons in the ball. correct Explanation: If a positively charged insulator is brought close to a conductor, it will attract some of the free electrons of the conductor closer to the insulator. The attraction between the insulator and the conductor results from the rearrangement of electrons. 002 10.0points A particle of mass 85 g and charge 39 μ C is released from rest when it is 19 cm from a second particle of charge 14 μ C. Determine the magnitude of the initial ac- celeration of the 85 g particle. Correct answer: 1599 . 21 m / s 2 . Explanation: Let : m = 85 g , q = 39 μ C = 3 . 9 × 10 5 C , d = 19 cm = 0 . 19 m , Q = 14 μ C = 1 . 4 × 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 3 . 9 × 10 5 C vextendsingle vextendsingle vextendsingle vextendsingle 1 . 4 × 10 5 C vextendsingle vextendsingle (0 . 085 kg) (0 . 19 m 2 ) = 1599 . 21 m / s 2 .

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