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9 - hernandez(ejh742 oldhomework 09 Turner(58120 This...

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hernandez (ejh742) – oldhomework 09 – Turner – (58120) 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 A 2 . 2 kg block initially at rest is pulled to the right along a horizontal, frictionless surface by a constant, horizontal force of 14 . 9 N. Find the speed of the block after it has moved 4 . 2 m. Correct answer: 7 . 54261 m / s. Explanation: Let : m = 2 . 2 kg , F = 14 . 9 N , and Δ x = 4 . 2 m . The acceleration of the block is a = F m = 14 . 9 N 2 . 2 kg = 6 . 77273 m / s 2 . Since the force is constant, the acceleration is constant. We find the final speed of the block using the equation v f = radicalBig v 2 0 + 2 a ( x f - x 0 ) = radicalBig 2 (6 . 77273 m / s 2 ) (4 . 2 m) = 7 . 54261 m / s . 002 (part 1 of 2) 10.0 points A string is tied to a book and pulled at an angle α as shown in the diagram. The book remains in contact with the table and does not move. m μ s T α Which choice best describes the free body diagram in the vertical direction for this situ- ation? 1. N = m g - T sin α correct 2. N = m g + T cos α 3. N = m g - T cos α 4. N = m g 5. N = m g + T sin α Explanation: m T string α m g N μ s N Because the string is pulling partially up, the force of the table on the book (the normal force) is less than if the string were not there. summationdisplay F y : N + T sin α = m g N = m g - T sin α . 003 (part 2 of 2) 10.0 points Which forces must change in order for the book to start moving? 1. friction 2. normal, friction, and tension in the string correct 3. friction and tension in the string 4. gravitational 5. normal and gravitational 6. None of these 7. normal 8. friction, tension in the string, and gravi- tational
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hernandez (ejh742) – oldhomework 09 – Turner – (58120) 2 9. tension in the string Explanation: The tension T
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