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Unformatted text preview: This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points What is the kinetic energy of a proton that is traveling at a speed of 3575 m / s? Take the mass of the proton to be 1 . 67 10- 27 kg. Correct answer: 1 . 06718 10- 20 J. Explanation: Since this speed is much less than the speed of light, we just use the approximate formula for kinetic energy: KE = 1 2 mv 2 = 1 2 (1 . 67 10- 27 kg)(3575 m / s) 2 = 1 . 06718 10- 20 J . 002 10.0 points If the kinetic energy of an electron is 5 . 3 10- 18 J, what is the speed of the elec- tron? You can use the approximate (non- relativistic) formula here. Take the mass of the electron to be 9 . 11 10- 31 kg. Correct answer: 3 . 41109 10 6 m / s. Explanation: The non-relativistic formula for kinetic en- ergy is KE = 1 2 mv 2 . Rearranging this expression to solve for the speed, we obtain v = 2( KE ) m = 2(5 . 3 10- 18 J) 9 . 11 10- 31 kg = 3 . 41109 10 6 m / s . 003 (part 1 of 4) 10.0 points Locations A , B , and C are in a region of uniform electric field, as shown in the diagram below. A B C % E Location A is at %r A =- . 7 , , m . Location B is at %r B = . 7 , , m . In the region the electric field has the value % E = 740 , , N / C . For a path starting at B and ending at A , the displacement vector % $ will be of the form % $ = x, , . Find x . Correct answer:- 1 . 4 m. Explanation: This is pretty straightforward. To find the vector pointing from B to A , we just subtract: % $ = %r A- %r B =- . 7 , , m- . 7 , , m =- 1 . 4 , , m . So x is just- 1 . 4 m . 004 (part 2 of 4) 10.0 points Now find the change in electric potential along this path. Correct answer: 1036 V. Explanation: We can just use the equation V =- % E % $. V =- E x x =- (740)(- 1 . 4) = 1036 V . 005 (part 3 of 4) 10.0 points Find the change in potential energy when a proton ( m p = 1 . 7 10- 27 kg and q p = 1 . 6 10- 19 C) moves from B to A . Correct answer: 1 . 6576 10- 16 J. Explanation: Here we can use the expression U = q V. U = q p V = (1 . 6 10- 19 C)(1036 V) = 1 . 6576 10- 16 J . 006 (part 4 of 4) 10.0 points Find the change in potential energy when an electron ( m e = 9 . 1 10- 31 kg and q e =- 1 . 6 10- 19 C) moves from B to A ....
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This note was uploaded on 10/25/2011 for the course PHY 303L taught by Professor Turner during the Spring '08 term at University of Texas at Austin.

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Ch17-h1-solutions - This print-out should have 20...

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