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Unformatted text preview: homework 02 HILL, WILLIAM Due: Sep 14 2007, 1:00 am 1 Question 1, chap 2, sect 1. part 1 of 1 10 points The average speed of an orbiting space shuttle is 21300 mi / h. The shuttle is orbit ing about 130 mi above the Earths surface. Assume the Earths radius is 3963 mi. How long does it take to circle the earth? Correct answer: 1 . 20737 h (tolerance 1 %). Explanation: The distance traveled by the space shuttle in one orbit is 2 (radius of the orbit) = 2 ( R e + h ) Hence, the required time is t = 2 ( R e + h ) v s = 2 (3963 mi + 130 mi) 21300 mi / h = 1 . 20737 h Question 2, chap 2, sect 1. part 1 of 1 10 points You plan a trip on which you want to aver age a speed of 92 km / h. You cover the first half of the distance at an average speed of only 57 km / h. What must be your average speed in the second half of the trip to meet your goal? Correct answer: 238 . 364 km / h (tolerance 1 %). Explanation: Basic Concepts If d is the total distance covered, then each half of the trip will cover a distance of d 2 . For the first half of the trip, t 1 = d 1 v 1 = 1 2 d v 1 = d 2 v 1 For the second half of the trip, t 2 = d 2 v 2 = 1 2 d v 2 = d 2 v 2 For the entire trip, t = t 1 + t 2 d v = d 2 v 1 + d 2 v 2 Multiplying by the LCD of (2 v v 1 v 2 ) yields 2 v 1 v 2 d = v v 2 d + v v 1 d 2 v 1 v 2 = v v 2 + v v 1 2 v 1 v 2 v v 2 = v v 1 Solving for v 2 we have v 2 = v v 1 2 v 1 v = (92 km / h)(57 km / h) 2(57 km / h) (92 km / h) = 238 . 364 km / h . Question 3, chap 2, sect 2. part 1 of 1 10 points The graph below shows the velocity v as a function of time t for an object moving in a straight line. t v t Q t R t S t P Which of the following graphs shows the corresponding displacement x as a function of time t for the same time interval? 1. t x t Q t R t S t P 2. t x t Q t R t S t P 3. t x t Q t R t S t P homework 02 HILL, WILLIAM Due: Sep 14 2007, 1:00 am 2 4. t x t Q t R t S t P 5. t x t Q t R t S t P 6. t x t Q t R t S t P 7. None of these graphs are correct. 8. t x t Q t R t S t P correct 9. t x t Q t R t S t P Explanation: The displacement is the integral of the ve locity with respect to time: vectorx = integraldisplay vectorv dt . Because the velocity increases linearly from zero at first, then remains constant, then de creases linearly to zero, the displacement will increase at first proportional to time squared, then increase linearly, and then increase pro portional to negative time squared. From these facts, we can obtain the correct answer. t x t Q t R t S t P Question 4, chap 2, sect 2. part 1 of 1 10 points An oceanic depthsounding vessel surveys the ocean bottom with ultrasonic waves that travel 1530 m / s in seawater....
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 Spring '08
 Turner
 Physics, Work

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