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Unformatted text preview: johnson (mjj622) HW 11 Coker (56625) 1 This printout should have 15 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. This assignment covers the fairly short Ch. 12, dealing with rigid body rotation, rota tional inertia and rotational kinetic energy. 001 10.0 points The tub of a washer goes into its spindry cycle, starting from rest and reaching an an gular speed of 2 rev / s in 3 . 2 s . At this point the person doing the laundry opens the lid, and a safety switch turns off the washer. The tub slows to rest in 6 . 4 s . Through how many revolutions does the tub turn? Assume constant angular accelera tion while it is starting and stopping. Correct answer: 9 . 6 rev. Explanation: Let : = 0 rev / s , 1 = 2 rev / s , t 1 = 3 . 2 s , 2 = 0 rev / s , and t 2 = 6 . 4 s . = av t = i + f 2 t = 1 2 t in each case since either the initial or final speed is zero. While speeding up, 1 = 2 rev / s 2 (3 . 2 s) = 3 . 2 rev and while decelerating, 2 = 2 rev / s 2 (6 . 4 s) = 6 . 4 rev , so = 1 + 2 = 3 . 2 rev + 6 . 4 rev = 9 . 6 rev . 002 (part 1 of 2) 10.0 points A disk with a radius of 0.1 m is spinning about its center with a constant angular speed of 10 rad/sec. What are the speed and magnitude of the acceleration of a bug clinging to the rim of the disk? 1. 0.1 m/s and 1 m/s 2 2. 10 m/s and 10 m/s 2 3. 1 m/s and 10 m/s 2 correct 4. 1 m/s and 0 m/s 2 (Disk spins at constant speed.) Explanation: The speed of the bug is v = R = (0 . 1 m)(10 1 / s) = 1 m / s and its acceleration is a r = R 2 = (0 . 1 m)(10 1 / s) 2 = 10 m / s 2 . 003 (part 2 of 2) 10.0 points Let the turntable spin faster and faster, with constant angular acceleration vector . Which sketch qualitatively shows the direc tion of the acceleration vector vectora of the bug? 1. vectora 2. vectora johnson (mjj622) HW 11 Coker (56625) 2 3. vectora correct 4. vectora Explanation: The bug has an acceleration vectora r directed toward the center of the circle, and an accel eration vectora t in the same direction as its velocity (counterclockwise); the net acceleration is the vector sum of vectora r and vectora t ....
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This note was uploaded on 02/10/2011 for the course PHY 303K taught by Professor Turner during the Fall '08 term at University of Texas.
 Fall '08
 Turner

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