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exam 1 phy - Version 151 Exam 1 chelikowsky(59005 This...

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Version 151 – 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. Both trains have the same velocity at some time before t B . correct 2. Both trains speed up all the time. 3. In the time interval from t = 0 to t = t B , train B covers more distance than train A. 4. Somewhere before time t B , both trains have the same acceleration. 5. At time t B , both trains have the same velocity. 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 3 . 4 s later with an initial speed of 66 . 64 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. 63.504 2. 92.7202 3. 150.932 4. 86.436 5. 48.6202 6. 120.062 7. 127.449 8. 159.201 9. 58.3222 10. 44.1 Correct answer: 127 . 449 m. Explanation: Δ t = 3 . 4 s , v 0 = 66 . 64 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 0 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 0 ( t 1 Δ t ) + g 2 ( t 1 Δ t ) 2 = v 0 ( t 1 Δ t ) + g 2 [ t 2 1 2 t 1 Δ t + (Δ t ) 2 ] ( v 0 g Δ t ) t 1 = v 0 Δ t g 2 t ) 2 t 1 = v 0 Δ t g 2 t ) 2 v 0 g Δ t = (66 . 64 m / s)(3 . 4 s) 1 2 (9 . 8 m / s 2 )(3 . 4 s) 2 66 . 64 m / s (9 . 8 m / s 2 ) (3 . 4 s) = 5 . 1 s , so the height of the house is y = g t 2 1 2 = (9 . 8 m / s 2 ) (5 . 1 s) 2 2 = 127 . 449 m .
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Version 151 – Exam 1 – chelikowsky – (59005) 2 003 10.0 points The distance between the sun and the Earth is about 1 . 5193 × 10 11 m. Express this distance in kilometers. 1. 1 . 5193 × 10 7 km 2. 1 . 5193 × 10 11 km 3. 1 . 5193 × 10 9 km 4. None of these 5. 1 . 5193 × 10 8 km correct 6. 1 . 5193 × 10 10 km 7. 1 . 5193 × 10 6 km Explanation: 1 km = 1 × 10 3 m , so distance = ( 1 . 5193 × 10 11 m ) · 1 km 1 × 10 3 m = 1 . 5193 × 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. Given an oil droplet with a mass of 8 . 41 × 10 7 kg and a density of 946 kg / m 3 that spreads out to form a circle with a radius of 44 . 4 cm on the water surface, what is the approximate diameter of an oil molecule? 1. 1.54414e-09 2. 1.43545e-09 3. 1.90383e-09 4. 2.05891e-09 5. 1.28881e-09 6. 1.56904e-09 7. 2.02061e-09 8. 1.51011e-09 9. 1.67256e-09 10. 1.64264e-09 Correct answer: 1 . 43545 × 10 9 m.
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