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# phys1hw2 - homework 02 ANDERSON ZACH Due Sep 8 2007 4:00 am...

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homework 02 – ANDERSON, ZACH – Due: Sep 8 2007, 4:00 am 1 Question 1, chap 2, sect 6. part 1 of 1 10 points An object was suspended in a fixed place ( y = 0) and then allowed to drop in a free fall. Taking up as the positive vertical direction, which of the following graphs correctly repre- sents its vertical motion as displacement vs time ? 1. t y correct 2. t y 3. t y 4. t y 5. t y 6. t y 7. t y 8. t y 9. t y 10. t y Explanation: The object is undergoing a constant down- ward gravitational acceleration g . The slope of a position vs time curve represents the velocity. Given g negationslash = 0 m / s 2 a < 0 m / s 2 a = g m / s 2 v 0 = 0 m / s y 0 = 0 m . Since y = y 0 + v 0 t + 1 2 a t 2 , therefore y = 1 2 g t 2 . This is a parabolic shaped curve starting a y = 0 with a continuously decreasing slope as time increases. Only the figure below is correct.

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homework 02 – ANDERSON, ZACH – Due: Sep 8 2007, 4:00 am 2 t y Question 2, chap 2, sect 1. part 1 of 2 10 points A student wanted to drive from Austin to San Antonio, 80 miles south of Austin on highway I35. Unfortunately, he entered the highway in the wrong direction and drove all the way to Waco — 100 miles north of Austin — before he noticed his error. In Waco, he turned around, drove back to Austin and continued to San Antonio. The whole trip took 6 . 7 hours. What was the student’s average speed dur- ing this trip? Correct answer: 41 . 791 MPH (tolerance ± 1 %). Explanation: Basic Concept : (average speed) = (total distance traveled) time The total distance traveled by the student is 100 miles from Austin to Waco, plus an- other 100 miles from Waco back to Austin, plus 80 miles from Austin to San Antonio, or 280 miles altogether. His average speed therefore is | v | = L t = 280 miles 6 . 7 hours = 41 . 791 MPH Question 3, chap 2, sect 1. part 2 of 2 10 points What was the student’s average velocity during his trip? Take your positive direction to be southbound on I35. Correct answer: 11 . 9403 MPH (tolerance ± 1 %). Explanation: Basic Concept : (average velocity) = (net displacement) time The student’s net displacement is from Austin to San Antonio — the fact that he went their by way of Waco is irrelevant for this question — or 80 miles in the positive southbound direction. His average velocity is therefore v = Δ X t = 80 miles 6 . 7 hours = 11 . 9403 MPH Question 4, chap 4, sect 4. part 1 of 3 10 points A boy is standing on a cliff. The boy’s hands are a height b above the ground level at the base of the cliff.. A monkey is in a tree. The monkey is at a height h above the boy’s hands. At t = 0 the boy throws a coconut upward at a speed v 0 , and at the same time the monkey releases his grip, falling downward to catch the coconut. Assume the initial speed of the monkey is 0 m/s, and the cliff is high enough so that the monkey is able to catch the coconut before hitting the ground.
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