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Unformatted text preview: klarin (sjk772) homework 02 Turner (56705) 1 This printout should have 13 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points Four point charges, each of magnitude 11 . 07 C, are placed at the corners of a square 76 . 8 cm on a side. If three of the charges are positive and one is negative, find the magnitude of the force experienced by the negative charge. The value of Coulombs constant is 8 . 98755 10 9 N m 2 / C 2 . Correct answer: 3 . 57441 N. Explanation: Let : k e = 8 . 98755 10 9 N m 2 / C 2 , d = 76 . 8 cm = 0 . 768 m , and Q = 11 . 07 C = 1 . 107 10 5 C . F 24 F 34 F 14 + 3 + 1 + 2 4 The forces are F 34 = F 24 = k e Q 2 d 2 = ( 8 . 98755 10 9 N m 2 / C 2 ) ( 1 . 107 10 5 C ) 2 (0 . 768 m) 2 = 1 . 8673 N , and F 14 = k e Q 2 ( 2 d ) 2 = 1 2 k e Q 2 d 2 = 1 2 F 34 . The vector sum of F 24 and F 34 is in the same direction as F 14 , so F = F 14 + radicalBig F 34 2 + F 24 2 = 1 2 F 34 + radicalBig 2 F 34 2 = parenleftbigg 1 2 + 2 parenrightbigg F 34 = parenleftbigg 1 2 + 2 parenrightbigg (1 . 8673 N) = 3 . 57441 N . 002 10.0 points A charge Q is spread uniformly along the circumference of a circle of radius R . A point charge q is placed at the center of this circle. What is the total force exerted on q as calculated by Coulombs law? 1. Use R for the distance. 2. None of these 3. Use 2 R for the distance. 4. The result of the calculation is zero. cor rect 5. Use 2 R for the distance. Explanation: By symmetry and using the fact that the charge is uniformly distributed along the cir cumference, the total force on q is zero. For example, consider a small element of charge Q on the circle. The force on q is along the vector connecting Q and q . But on the ex act opposite side there is another element of charge Q which exerts an equal but opposite force on q . This is true for every point on the circle, so the net force is zero. 003 10.0 points A charge q 1 of 4 . 00 10 9 C and a charge q 2 of 2 . 30 10 9 C are separated by a distance of 45 . 0 cm....
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This note was uploaded on 10/10/2010 for the course PHY 56705 taught by Professor Turner during the Fall '10 term at University of Texas at Austin.
 Fall '10
 Turner
 Charge, Work

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