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Ch10 HW3

# Ch10 HW3 - WebAssign Ch10 HW3(Homework Current Score 57 out...

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Ch10 HW3 (Homework) Arthur Barfield PHYS 2211, section M, Fall 2008 Instructor: Jennifer Curtis Web Assign Current Score: 57 out of 57 Due: Monday, November 10, 2008 09:00 AM EST Description Torque; Angular impulse; Systems with zero torque Instructions Reading: Section 10.3-10.7 In this assignment you may submit each question part separately. Three submissions are allowed for numerical answers, and two submissions for multiple choice answers. The due date for this assignment is past. Your work can be viewed below, but no changes can be made. 1. [MI2 10.X.23] 7.5/7.5 points A uniform solid disk with radius 11 cm has mass 0.8 kg (moment of inertia I = ½ MR 2 ). A constant force 12 N is applied as shown. At the instant shown, the angular velocity of the disk is 40 radians/s in the direction (where + x is to the right, + y is up, and + z is out of the page, toward you). The length of the string d is 19 cm. At this instant, what are the magnitude and direction of the angular momentum about the center of the disk? = .1936 0.194 kg · m 2 /s Direction: -z -z What are the magnitude and direction of the torque on the disk, about the center of mass of the disk? = 1.32 1.32 N · m Direction: -z -z

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The string is pulled for 0.2 s. What are the magnitude and direction of the angular impulse applied to the disk during this time? = .264 0.264 N · m · s Direction: -z -z After the torque has been applied for 0.2 s, what are the magnitude and direction of the angular momentum about the center of the disk? .458 0.458 kg · m 2 /s Direction: -z -z At this later time, what are the magnitude and direction of the angular velocity of the disk? 94.55 94.5 rad/s Direction: -z -z Solution or Explanation 2. [MI2 10.X.21.alt01] 5.5/5.5 points A rotating uniform-density disk of radius 0.6 m is mounted in the vertical plane. The axle is held up by supports that are not shown, and the disk is free to rotate on the nearly frictionless axle. The disk has mass 3.8 kg. A lump of clay with mass 0.3 kg falls and sticks to the outer edge of the wheel at the location < -0.36 , 0.480 , 0 > m. Just before the impact the clay has a speed 6 m/s, and the disk is rotating clockwise with angular speed 0.28 radians/s. (a) Just before the impact, what is the angular momentum of the combined system of wheel plus
clay about the center C ? (As usual, x is to the right, y is up, and z is out of the screen, toward you.) C,i = < 0 0 , 0 0 , .4565 0.456 > kg · m 2 /s (b) Just after the impact, what is the angular momentum of the combined system of wheel plus clay about the center C ? C,f = < 0 0 , 0 0 , .4565 0.456 > kg · m 2 /s (c) Just after the impact, what is the angular velocity of the wheel? f = < 0 0 , 0 0 , .5763 0.576 > radians/s (d) Qualitatively, what happens to the linear momentum of the combined system? (Think about why this is.) There is no change because linear momentum is always conserved.

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Ch10 HW3 - WebAssign Ch10 HW3(Homework Current Score 57 out...

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