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Unformatted text preview: Version 010 exam1 bohm (59970) 1 This print-out should have 11 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points You and your friend throw balloons filled with water from the roof of a several story apart- ment house. You simply drop a balloon from rest. A second balloon is thrown downward by your friend 3 . 3 s later with an initial speed of 64 . 68 m / s. They hit the ground simultane- ously. The acceleration of gravity is 9 . 8 m / s 2 . You can neglect air resistance. How high is the apartment house? 1. 68.9062 2. 159.201 3. 167.69 4. 53.361 5. 127.449 6. 80.3723 7. 44.1 8. 74.529 9. 142.884 10. 120.062 Correct answer: 120 . 062 m. Explanation: For balloon 1: y 1 = 1 2 g t 2 1 For balloon 2: y 2 = v t 2 + g t 2 2 2 Balloon 2 is thrown t seconds after balloon 1 and they hit the ground at the same time, so: t 1 = t 2 + t Since the height of the house is the same for both of the balloons, y 1 = y 2 g t 2 1 2 = v ( t 1- t ) + g 2 ( t 1- t ) 2 ( v- g t ) t 1 = v t- g 2 t 2 t 1 = v t- g 2 t 2 v- g t = t 2 + v v- g t t 2 For t = 2 s t 1 = 1 + v v- 2 g For v = 30 m/s, t = 2 s t 1 = 4 . 95 s From the above, once t 1 is known, the height of the house is given simply by y = g t 2 1 2 For t 1 = 4 . 95 s, y = 120 . 062 m 002 10.0 points Three vectors vector A , vector B , and vector C have the following x and y components: A x = 7 . 9, A y =- 6 . 3; B x =- 3 . 8, B y = 4 . 5; C x = 2 . 7, C y = 5 . 7. What is the magnitude of vector A + vector B + vector C ? 1. 8.5235 2. 8.27345 3. 2.33452 4. 3.80132 5. 9.45569 6. 7.83901 7. 2.06155 8. 3.67967 9. 10.5385 10. 5.59017 Correct answer: 7 . 83901. Explanation: Given : vector A = (7 . 9 ,- 6 . 3) , vector B = (- 3 . 8 , 4 . 5) , and vector C = (2 . 7 , 5 . 7) . Version 010 exam1 bohm (59970) 2 Let vector D = vector A + vector B + vector C . The x component o f vector D is D x = A x + B x + C x = 7 . 9+(- 3 . 8)+2 . 7 = 6 . 8 and the y component of vector D is D y = A y + B y + C y =- 6 . 3+4 . 5+5 . 7 = 3 . 9 . Thus the magnitude of vector A + vector B + vector C is given by D = radicalBig D 2 x + D 2 y = radicalbig 6 . 8 2 + 3 . 9 2 = 7 . 83901 ....
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This note was uploaded on 11/03/2008 for the course PHY 302K taught by Professor Kaplunovsky during the Spring '08 term at University of Texas at Austin.

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exam1-solutions - Version 010 exam1 bohm (59970) 1 This...

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