Exam 1-solutions

Exam 1-solutions - Version 147 – Exam 1 – chelikowsky...

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Unformatted text preview: Version 147 – Exam 1 – chelikowsky – (59005) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points The graph shows position as a function of time for two trains running on parallel tracks. At time t = 0 the position of both trains is 0 (at the origin). position time t B B A Which is true? 1. In the time interval from t = 0 to t = t B , train B covers more distance than train A. 2. At time t B , both trains have the same velocity. 3. Both trains have the same velocity at some time before t B . correct 4. Both trains speed up all the time. 5. Somewhere before time t B , both trains have the same acceleration. Explanation: The slope of the curve B is parallel to line A at some point t < t B . 002 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 2 . 2 s later with an initial speed of 43 . 12 m / s. They hit the ground simultane- ously. How high is the apartment house? The acceleration of gravity is 9 . 8 m / s 2 . Neglect air resistance. 1. 68.9062 2. 135.056 3. 53.361 4. 127.449 5. 142.884 6. 86.436 7. 112.896 8. 92.7202 9. 99.225 10. 120.062 Correct answer: 53 . 361 m. Explanation: Δ t = 2 . 2 s , v = 43 . 12 m / s , and g = 9 . 8 m / s 2 . For balloon 1 y 1 = 1 2 g t 2 1 , and for balloon 2 y 2 = v t 2 + g t 2 2 2 . Balloon 2 is thrown Δ t sec- onds after balloon 1 and they hit the ground at the same time, so t 1 = t 2 + Δ t and y 1 = y 2 g t 2 1 2 = v ( t 1 − Δ t ) + g 2 ( t 1 − Δ t ) 2 = v ( t 1 − Δ t ) + g 2 [ t 2 1 − 2 t 1 Δ t + (Δ t ) 2 ] ( v − g Δ t ) t 1 = v Δ t − g 2 (Δ t ) 2 t 1 = v Δ t − g 2 (Δ t ) 2 v − g Δ t = (43 . 12 m / s)(2 . 2 s) − 1 2 (9 . 8 m / s 2 )(2 . 2 s) 2 43 . 12 m / s − (9 . 8 m / s 2 ) (2 . 2 s) = 3 . 3 s , so the height of the house is y = g t 2 1 2 = (9 . 8 m / s 2 ) (3 . 3 s) 2 2 = 53 . 361 m . Version 147 – Exam 1 – chelikowsky – (59005) 2 003 10.0 points The distance between the sun and the Earth is about 1 . 4961 × 10 11 m. Express this distance in kilometers. 1. 1 . 4961 × 10 10 km 2. 1 . 4961 × 10 6 km 3. 1 . 4961 × 10 11 km 4. 1 . 4961 × 10 7 km 5. None of these 6. 1 . 4961 × 10 9 km 7. 1 . 4961 × 10 8 km correct Explanation: 1 km = 1 × 10 3 m , so distance = ( 1 . 4961 × 10 11 m ) · 1 km 1 × 10 3 m = 1 . 4961 × 10 8 km . 004 10.0 points You can obtain a rough estimate of the size of a molecule with the following simple exper- iment: Let a droplet of oil spread out on a fairly large but smooth water surface. The re- sulting ”oil slick” that forms on the surface of the water will be approximately one molecule thick....
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This note was uploaded on 07/07/2010 for the course PHY 302 taught by Professor Staff during the Summer '08 term at University of Texas.

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Exam 1-solutions - Version 147 – Exam 1 – chelikowsky...

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