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Unformatted text preview: homework 02 ARMSTRONG, DOMINIC Due: Sep 18 2007, 3:00 am 1 Question 1, chap 2, sect 6. part 1 of 3 10 points Given: The acceleration of gravity on Earth is 9 . 8 m / s 2 . Consider a ball thrown up from the ground (the point O). It passes a window (the seg ment AB) in the time interval 0 . 321 s (see the figure). The points in the figure represent the sequential order, and are not drawn to scale. The distance AB = 0 . 87 m. O C B A . 87 m b b b b b b b b b b b x y Find the average speed as the ball passes the window. Correct answer: 2 . 71028 m / s (tolerance 1 %). Explanation: Basic Concepts: vectora = vectorv t For constant acceleration v = s t = v i + v f 2 v = v + a t . For the acceleration of gravity ( a = g ) v = v g t . Solution: The average velocity is given by v = s t =  AB  t = . 87 m . 321 s = 2 . 71028 m / s . Alternative Part 1: d = y B y A = v A t 1 2 g t 2 v A = d + 1 2 g t 2 t = . 87 m + 1 2 (9 . 8 m / s 2 ) (0 . 321 s) 2 (0 . 321 s) = 4 . 28318 m / s v B = v A g t = 4 . 28318 m / s (9 . 8 m / s 2 ) (0 . 321 s) = 1 . 13738 m / s v = v A + v B 2 = 4 . 28318 m / s + 1 . 13738 m / s 2 = 2 . 71028 m / s . Question 2, chap 2, sect 6. part 2 of 3 10 points What is the magnitude of the decrease of the velocity from A to B? Correct answer: 3 . 1458 m / s (tolerance 1 %). Explanation: For a constant acceleration vectora = vectorv t , =  vectorv  =  vectora t  = g t . Thus the decrease in velocity is v = g t = (9 . 8 m / s 2 )(0 . 321 s) = 3 . 1458 m / s . Alternative Part 2: v = v A v B = 4 . 28318 m / s 1 . 13738 m / s = 3 . 1458 m / s . homework 02 ARMSTRONG, DOMINIC Due: Sep 18 2007, 3:00 am 2 Question 3, chap 2, sect 6. part 3 of 3 10 points If the ball continues its path upward with out obstruction, find the travel time between B and C, where point C is at the balls maxi mum height....
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This homework help was uploaded on 04/07/2008 for the course PHY 301 taught by Professor Swinney during the Fall '07 term at University of Texas at Austin.
 Fall '07
 Swinney
 mechanics, Acceleration, Gravity, Work

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