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# 4 - hernandez(ejh742 oldhomework 04 Turner(58120 This...

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hernandez (ejh742) – oldhomework 04 – Turner – (58120) 1 This print-out should have 12 questions. Multiple-choice 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 0 = 17 m. 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 8 9 v ( t ) time ( × 1 s) velocity ( × 3 m / 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 particle’s velocity decreases from the initial v 0 = 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 0 + v f 2 = 12 m / s + 3 m / s 2 = 7 . 5 m / s , the particle’s displacement is Δ x = t · ¯ v = (4 s) (7 . 5 m / s) = 30 m , and its final position x = x 0 + Δ x = 17 m + 30 m = 47 m . 002 (part 2 of 2) 10.0 points What is the particle’s acceleration? Correct answer: - 2 . 25 m / s 2 . Explanation: The average acceleration of the particle is ¯ a = Δ v Δ t = v f - v 0 t = 3 m / s - 12 m / s 4 s = - 2 . 25 m / s 2 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, 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 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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4 - hernandez(ejh742 oldhomework 04 Turner(58120 This...

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