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EPChap10-Solution2 - 6 Chap 10 HW2 Questions 5 Figure...

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6 6 Chap. 10 HW2 Questions 5. Figure 10-25 a is an overhead view of a horizontal bar that can pivot; two horizontal forces act on the bar, but it is stationary. If the angle between the bar and F 2 is now decreased from 90° and the bar is still not to turn, should F 2 be made larger, made smaller, or left the same? When the angle is decreased the torque due to F 2 is now reduced. Therefore F 2 should be made larger. 9. Figure 10-28 shows three flat disks (of the same radius) that can rotate about their centers like merry-go- rounds. Each disk consists of the same two materials, one denser than the other (density is mass per unit volume). In disks 1 and 3, the denser material forms the outer half of the disk area. In disk 2, it forms the inner half of the disk area. Forces with identical magnitudes are applied tangentially to the disk, either at the outer edge or at the interface of the two materials, as shown. Rank the disks according to (a) the torque about the disk center, (b) the rotational inertia about the disk center, and (c) the angular acceleration of the disk, greatest first. a) All the F ’s are the same and are directed tangentially. The distances from the center varies leading to different torques. The ranking is 1 and 2 tie, then 3. b) More mass further from the center leads to larger moment of inertia. The ranking is 1 and 3 tie, then 2 c) Since 2 has the smallest moment of inertia and one of the largest torques, its angular acceleration is largest. Since 3 has one of the smallest moments of inertia and the the smallest torque, its angular acceleration is smallest. The ranking is 2, 1,3
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