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Exam1-solutions

# Exam1-solutions - Version 050 Exam1 markert(56480 This...

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Version 050 – Exam1 – markert – (56480) 1 This print-out should have 14 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A rock is thrown downward from an unknown height above the ground with an initial speed of 24 m / s. It strikes the ground 8 . 6 s later. Determine the initial height of the rock above the ground. The acceleration of gravity is 9 . 8 m / s 2 . 1. 327.236 2. 513.6 3. 568.804 4. 33.649 5. 88.704 6. 283.296 7. 296.704 8. 254.464 9. 144.624 10. 491.404 Correct answer: 568 . 804 m. Explanation: Consider down to be positive. Let : g = 9 . 8 m / s 2 , v 0 = 24 m / s , and t = 8 . 6 s . h = h 0 - v 0 t - 1 2 g t 2 = 0 h 0 = v 0 t + 1 2 g t 2 = (24 m / s) (8 . 6 s) + 1 2 (9 . 8 m / s 2 ) (8 . 6 s) 2 = 568 . 804 m . 002 10.0 points The graph shows the velocity v as a function of time t for an object moving in a straight line. t v 0 t Q t R t S t P Which graph shows the corresponding dis- placement x as a function of time t for the same time interval? 1. t x 0 t Q t R t S t P 2. t x 0 t Q t R t S t P 3. t x 0 t Q t R t S t P correct 4. t x 0 t Q t R t S t P 5. t x 0 t Q t R t S t P 6. t x 0 t Q t R t S t P 7. t x 0 t Q t R t S t P 8. None of these graphs is correct. 9. t x 0 t Q t R t S t P Explanation:

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Version 050 – Exam1 – markert – (56480) 2 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 0 t Q t R t S t P 003 10.0 points A hunter wishes to cross a river that is 1 . 51 km wide and flows with a speed of 2 . 19 km / h parallel to its banks. The hunter uses a small powerboat that moves at a maximum speed of 9 . 13 km / h with respect to the water.
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