oldhw4 - oldhomework 04 Turner (58185) This print-out...

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print-out should have 12 questions. Multiple-choice questions may continue on the next column or page – fnd 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 5 s per division and on the vertical axis 1 m / s per division. 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 8 9 v ( t ) time ( × 5 s) velocity( × 1m / s) Initially, at t = 0 the particle is at x 0 = 31 m. What is the position x oF the particle at time t = 20 s? Correct answer: 81 m. Explanation: Looking at the v ( t ) plot we see that over time t = 4 × 5 s = 20 s, the particle’s velocity decreases From the initial v 0 = 4 × 1 m / s = 4 m / s to fnal v f = 1 × 1 m / s = 1 m / s . The v ( t ) line is straight, which indicates constant deceleration rate, hence the average velocity is given by ¯ v = v 0 + v f 2 = 2 . 5 m / s . Consequently, the particle’s displacement during this time is simply Δ x = t × ¯ v = 50 m , and its fnal position x = x 0 + Δ x = 81 m . 002 (part 2 oF 2) 10.0 points What is the particle’s acceleration? Correct answer: - 0 . 15 m / s 2 . Explanation: The average acceleration oF the particle is ¯ a = Δ v Δ t = v f - v 0 t = - 0 . 15 m / s 2 . Since the v ( t ) line is straight, the acceleration is constant, hence a = ¯ a = - 0 . 15 m / s 2 . 003 (part 1 oF 2) 10.0 points A speeder passes a parked police car at 33.3 m/s. Instantaneously, the police car starts From rest with a uniForm acceleration oF 2.43 m/s 2 . a) How much time pases beFore the speeder is overtaken by the police car? Correct answer: 27 . 4074 s. Explanation: Basic Concepts: ±or the speeder, Δ x s = v s Δ t ±or the policeman, v i = 0 m/s, so the equa- tion simplifes to Δ x p = 1 2 a p t ) 2 Let : v s = 33 . 3 m / s v i,p = 0 m / s a p = 2 . 43 m / s 2 . Solution: Δ x s = Δ x p v s Δ t = 1 2 a p t ) 2 2 v s Δ t = a p t ) 2 2 v s = a p Δ t Δ t = 2 v s a p = 2(33 . 3 m / s) 2 . 43 m / s 2 = 27 . 4074 s . oldhomework 04 – Turner – (58185)
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This note was uploaded on 03/26/2010 for the course PHY 303K taught by Professor Turner during the Fall '08 term at University of Texas at Austin.

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oldhw4 - oldhomework 04 Turner (58185) This print-out...

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