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Unformatted text preview: hernandez (ejh742) oldhomework 04 Turner (58120) 1 This printout should have 12 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points The velocity v ( t ) of some particle is plotted as a function of time on the graph below. The scale on the horizontal axis is 1 s per division and on the vertical axis 3 m / s per division. Initially, the particle is at x = 17 m. 1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 v ( t ) time ( 1 s) velocity( 3m / s) What is the position x of the particle at time t = 4 s? Correct answer: 47 m. Explanation: Looking at the v ( t ) plot we see that over time t = 4 (1 s) = 4 s, the particles velocity decreases from the initial v = 4 (3 m / s) = 12 m / s to final v f = 1 (3 m / s) = 3 m / s . The v ( t ) line is straight, which indicates constant deceleration rate, so the average velocity is given by v = v + v f 2 = 12 m / s + 3 m / s 2 = 7 . 5 m / s , the particles displacement is x = t v = (4 s) (7 . 5 m / s) = 30 m , and its final position x = x + x = 17 m + 30 m = 47 m . 002 (part 2 of 2) 10.0 points What is the particles acceleration? Correct answer: 2 . 25 m / s 2 . Explanation: The average acceleration of the particle is a = v t = v f v t = 3 m / s 12 m / s 4 s = 2 . 25 m / s Since the v ( t ) line is straight, the acceleration is constant, so a = a = 2 . 25 m / s 2 . 003 (part 1 of 2) 10.0 points A speeder passes a parked police car at 25.7 m/s. Instantaneously, the police car starts from rest with a uniform acceleration of 2.45 m/s 2 . a) How much time pases before the speeder is overtaken by the police car? Correct answer: 20 . 9796 s. Explanation: Basic Concepts: For the speeder, x s = v s t For the policeman, v i = 0 m/s, so the equa tion simplifies to x p = 1 2 a p ( t ) 2 Let : v s = 25 . 7 m / s v i,p = 0 m / s a p = 2 . 45 m / s 2 ....
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This note was uploaded on 06/14/2011 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.
 Spring '08
 Turner
 Physics, Work

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