Homework 4-solutions

# Homework 4-solutions - kumar(vk4433 Homework 4...

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kumar (vk4433) – Homework 4 – markert – (55325) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points The potential difference between a storm cloud and the ground is 1 . 04 × 10 8 V. If a bolt carrying 5 C falls from a cloud to Earth, what is the magnitude of the change of potential energy of the charge? Correct answer: 5 . 2 × 10 8 J. Explanation: Let : V = 1 . 04 × 10 8 V and q = 5 C . The potential energy is U = V q = (1 . 04 × 10 8 V )(5 C ) = 5 . 2 × 10 8 J . 002 10.0points In a charging process, 2 × 10 13 electrons are removed from one small metal sphere and placed on a second identical sphere. Initially both metal spheres were neutral. After the charging process the electrical potential en- ergy associated with the two spheres is found to be 0 . 069 J . What is the distance between the two spheres? The value of the Coulomb constant is 8 . 98755 × 10 9 N · m 2 / C 2 and the elemental charge is 1 . 6 × 10 19 C . Correct answer: 1 . 3338 m. Explanation: Let : n = 2 × 10 13 , q e = 1 . 6 × 10 19 C , U e = 0 . 069 J , and k e = 8 . 98755 × 10 9 N · m 2 / C 2 . q 1 = n q e and q 2 = n q e , so U e = k e q 1 q 2 r r = k e q 1 q 2 U e = k e ( n q e ) 2 U e = (8 . 98755 × 10 9 N · m 2 / C 2 ) × (2 × 10 13 ) 2 (1 . 6 × 10 19 C) 2 0 . 069 J = 1 . 3338 m . 003(part1of2)10.0points Find the speed of an electron that has a kinetic energy of 1 . 19 eV. 1 eV= 1 . 602 × 10 19 J . Correct answer: 6 . 4697 × 10 5 m / s. Explanation: Let : E k = 1 . 19 eV and m e = 9 . 109 × 10 31 kg . The kinetic energy is E k = 1 2 m e v 2 e v e = radicalbigg 2 K e m e = radicalBigg 2(1 . 19 eV) 9 . 109 × 10 31 kg 1 . 602 × 10 19 J 1 eV = 6 . 4697 × 10 5 m / s . 004(part2of2)10.0points Calculate the speed of a proton with a kinetic energy of 1 . 19 eV. Correct answer: 15098 . 1 m / s. Explanation: Let : E k = 1 . 19 eV and m p = 1 . 6726 × 10 27 kg .

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