hw5 - This print-out should have 12 questions....

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Unformatted text preview: 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 3) 10.0 points Two cars are traveling along a straight line in the same direction, the lead car at 28 m / s and the other car at 41 m / s. At the moment the cars are 55 m apart, the lead driver applies the brakes, causing the car to have an acceleration of − 2 . 0 m/s 2 . a) How long does it take for the lead car to stop? Correct answer: 14 s. Explanation: Basic Concept: a avg = v f − v i Δ t = − v i Δ t since v f = 0 m/s. Given: v i, 1 = +28 m / s v f, 1 = 0 m / s a 1 = − 2 . 0 m / s 2 Solution: Δ t 1 = − v i, 1 a 1 = − 28 m / s − 2 m / s 2 = 14 s 002 (part 2 of 3) 10.0 points Assume that the driver of the chasing car applies the brakes at the same time as the driver of the lead car. b) What must the chasing car’s minimum negative acceleration be to avoid hitting the lead car? Correct answer: − 3 . 34861 m / s 2 . Explanation: Basic Concepts: The equations simplify to Δ x = 1 2 ( v f + v i ) Δ t = v i 2 Δ t and 0 = v 2 i + 2 a Δ x since v f = 0 m/s. Given: v i, 2 = +41 m / s v f, 2 = 0 m / s Δ x 2 = Δ x 1 + 55 m Δ t 2 = Δ t 1 = 14 s Solution: The lead car traveled Δ x 1 = 28 m / s 2 (14 s) = 196 m The chasing car traveled Δ x 2 = 196 m + 55 m = 251 m with a minimum acceleration of a 2 = − v 2 i, 2 2Δ x 2 = − (41 m / s) 2 2(251 m) = − 3 . 34861 m / s 2 003 (part 3 of 3) 10.0 points c) How long does it take the chasing car to stop? Correct answer: 12 . 2439 s. Explanation: Basic Concepts: a = v f − v i Δ t = − v i Δ t since v f = 0 m/s. Given: v i, 2 = 41 m / s a 2 = − 3 . 34861 m / s 2 Solution: Δ t 2 = − v i, 2 a 2 = − 41 m / s − 3 . 34861 m / s 2 = 12 . 2439 s homework 05 – Turner – (58185) 1 hinojosa (jlh3938) – homework 05 – Turner – (58185) 2 004 (part 1 of 2) 10.0 points Throw a ball upward from point O with an initial speed of 66 m / s....
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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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hw5 - This print-out should have 12 questions....

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