# h5 - hernandez(ejh742 – homework 05 – Turner –(58120...

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Unformatted text preview: hernandez (ejh742) – homework 05 – 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 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 39 m / s. At the moment the cars are 56 m apart, the lead driver applies the brakes, causing the car to have an acceleration of − 2 . 5 m/s 2 . a) How long does it take for the lead car to stop? Correct answer: 11 . 2 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 . 5 m / s 2 Solution: Δ t 1 = − v i, 1 a 1 = − 28 m / s − 2 . 5 m / s 2 = 11 . 2 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 . 57378 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 = +39 m / s v f, 2 = 0 m / s Δ x 2 = Δ x 1 + 56 m Δ t 2 = Δ t 1 = 11 . 2 s Solution: The lead car traveled Δ x 1 = 28 m / s 2 (11 . 2 s) = 156 . 8 m The chasing car traveled Δ x 2 = 156 . 8 m + 56 m = 212 . 8 m with a minimum acceleration of a 2 = − v 2 i, 2 2Δ x 2 = − (39 m / s) 2 2(212 . 8 m) = − 3 . 57378 m / s 2 003 (part 3 of 3) 10.0 points c) How long does it take the chasing car to stop? Correct answer: 10 . 9128 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 = 39 m / s a 2 = − 3 . 57378 m / s 2 Solution: Δ t 2 = − v i, 2 a 2 = − 39 m / s − 3 . 57378 m / s 2 = 10 . 9128 s hernandez (ejh742) – homework 05 – Turner – (58120) 2 004 (part 1 of 2) 10.0 points Throw a ball upward from point O with an initial speed of 52 m...
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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.

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h5 - hernandez(ejh742 – homework 05 – Turner –(58120...

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