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Unformatted text preview: gonzalez (ng4897) – 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 4 s per division and on the vertical axis 9 m / s per division. Initially, the particle is at x = 72 m. 1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 v ( t ) time ( × 4 s) velocity( × 9m / s) What is the position x of the particle at time t = 16 s? Correct answer: 432 m. Explanation: Looking at the v ( t ) plot we see that over time t = 4 (4 s) = 16 s, the particle’s velocity decreases from the initial v = 4 (9 m / s) = 36 m / s to final v f = 1 (9 m / s) = 9 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 = 36 m / s + 9 m / s 2 = 22 . 5 m / s , the particle’s displacement is Δ x = t · ¯ v = (16 s) (22 . 5 m / s) = 360 m , and its final position x = x + Δ x = 72 m + 360 m = 432 m . 002 (part 2 of 2) 10.0 points What is the particle’s acceleration? Correct answer: 1 . 6875 m / s 2 . Explanation: The average acceleration of the particle is ¯ a = Δ v Δ t = v f v t = 9 m / s 36 m / s 16 s = 1 . 6875 m Since the v ( t ) line is straight, the acceleration is constant, so a = ¯ a = 1 . 6875 m / s 2 . 003 (part 1 of 2) 10.0 points A speeder passes a parked police car at 30.1 m/s. Instantaneously, the police car starts from rest with a uniform acceleration of 2.41 m/s 2 . a) How much time pases before the speeder is overtaken by the police car? Correct answer: 24 . 9793 s. Explanation: Basic Concepts: For the speeder, Δ x s = v s Δ t For the policeman, v i = 0 m/s, so the equa tion simplifies to Δ x p = 1 2 a p (Δ t ) 2 Let : v s = 30 . 1 m / s v i,p = 0 m / s a p = 2 . 41 m / s 2 ....
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This note was uploaded on 03/10/2010 for the course EE PHY 303K taught by Professor Gordito during the Spring '10 term at École Normale Supérieure.
 Spring '10
 GORDITO

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