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Ch10 HW3 S2008

# Ch10 HW3 S2008 - Ch10 HW3 S2008 10:34 AM Web Assign Ch10...

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4/25/08 10:34 AM Ch10 HW3 S2008 Page 1 of 11 http://www.webassign.net/[email protected]/[email protected] Ch10 HW3 S2008 (Homework) KRISTIN SEILOFF PHYS 2211 M & N Spring 08, section N05, Spring 2008 Instructor: Jennifer Curtis 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. Web Assign Current Score: 50 out of 61 Due: Monday, April 7, 200808:35 AM EDT 1. 4/4 points As shown in the diagram below, seven forces all with magnitude | | = 33 N are applied to an irregularly shaped object. Each force is applied at a different location on the object, indicated by the tail of the arrow; the directions of the forces differ. The distances shown in the diagram have these values: w = 15 m, h = 24 m, and d = 23 m. For each force, calculate the z component of the torque due to that force, relative to location A (x to the right, y up, z out of the page). Make sure you give the correct sign. (1) A,1,z = -792 -792 N · m (2) A,2,z = -792 -792

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4/25/08 10:34 AM Ch10 HW3 S2008 Page 2 of 11 http://www.webassign.net/[email protected]/[email protected] N · m (3) A,3,z = -792 -792 N · m (4) A,4,z = -495 -495 N · m (5) A,5,z = 0 0 N · m (6) A,6,z = 0 0 N · m (7) A,7,z = 759 759 N · m Relative to location A , what is the z component of the net torque acting on this object? A,net,z = -2112 -2110 N · m Solution or Explanation The magnitude of the torque is r | |, and the sign of the z component is determined using the right-hand rule. 2. 7.5/7.5 points A uniform solid disk with radius 9 cm has mass 0.9 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 25 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? = .0911 0.0911 kg·m 2 /s Direction: -z -z
4/25/08 10:34 AM Ch10 HW3 S2008 Page 3 of 11 http://www.webassign.net/[email protected]/student[email protected] What are the magnitude and direction of the torque on the disk, about the center of mass of the disk? = 1.08 1.08 N · m Direction: -z -z 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? = .216 0.216 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? .3071 0.307 kg·m 2 /s Direction: -z -z At this later time, what are the magnitude and direction of the angular velocity of the disk? 84.3 84.3 rad/s Direction: -z -z Solution or Explanation 3. 7/7 points Two people of different masses sit on a seesaw. M 1 , the mass of person 1 is 91 kg, M 2 is 45 kg, d 1 = 0.8 m, and d 2 = 1.3 m. The mass of the board is negligible.

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4/25/08 10:34 AM Ch10 HW3 S2008 Page 4 of 11 http://www.webassign.net/[email protected]/[email protected] (a) What is the magnitude of the torque about the pivot (location A ) due to the gravitational force on person 1?
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