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Unformatted text preview: Version 057 – exam1 – markert – (58840) 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 An object is shot vertically upward into the air with a positive initial velocity. Which of the following correctly describes the velocity and acceleration of the object at its maximum elevation? Velocity Acceleration 1. negative negative 2. zero negative correct 3. zero zero 4. positive positive 5. positive negative Explanation: At the maximum elevation, the vertical ve- locity is zero. The acceleration is due to gravity, which acts down. 002 10.0 points Identify all graphs that represent motion at constant speed (note the axes carefully). a) t x b) t v c) t a d) t v e) t a 1. d) only 2. e only 3. a) and c) 4. a), b), and e) 5. a only 6. None of these 7. a, b), and c) 8. a) and d) correct 9. a), b), and d) 10. c only Explanation: For constant speed, a = 0 . a) x = k t, k > 0, increases at a constant rate, so it has a constant velocity. b) v = k t, k > 0, increases at a constant rate, so it has a constant acceleration. c) a = k t, k > 0, increases at a constant rate. d) v = k, k > 0, so it represents a constant velocity. e) a = k, k > 0, so it represents a constant, nonzero acceleration. 003 10.0 points A car traveling at 6.6 m/s accelerates 4.1 m/s 2 to reach a speed of 13.0 m/s. How long does it take for this acceleration Version 057 – exam1 – markert – (58840) 2 to occur? 1. 0.72973 2. 2.44444 3. 4.14286 4. 1.65789 5. 2.52 6. 1.89189 7. 1.56098 8. 1.83333 9. 2.25714 10. 1.74286 Correct answer: 1 . 56098 s. Explanation: Basic Concept: a avg = Δ v Δ t Given: v i = 6 . 6 m / s a avg = 4 . 1 m / s 2 v f = 13 . 0 m / s Solution: Δ t = Δ v a avg = v f- v i a avg = 13 m / s- 6 . 6 m / s 4 . 1 m / s 2 = 1 . 56098 s Dimensional analysis for Δ t : m s ÷ m s 2 = m s · s 2 m = s 004 10.0 points Two 25 N forces and a 50 N force act on a hanging box as shown. 25 N 25 N 50 N Will the box experience acceleration? 1. No; it is balanced. 2. Unable to determine without the angle. 3. Yes; downward. correct 4. Yes; upward. Explanation: The horizontal components of the two 25 N forces cancel, leaving an upward force that is less than 50 N. Thus, the net force on the box is down, causing it to accelerate downward....
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This note was uploaded on 10/04/2009 for the course PHY 58840 taught by Professor Markert during the Fall '09 term at University of Texas at Austin.
- Fall '09