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Unformatted text preview: homework 19 FIERRO, JEFFREY Due: Apr 6 2008, 11:00 pm 1 Question 1, chap 13, sect 4. part 1 of 1 10 points A solid steel sphere of density 7 . 85 g / cm 3 and mass 0 . 7 kg spins on an axis through its center with a period of 2 . 4 s. Given V sphere = 4 3 R 3 , what is its angular momentum? Correct answer: 0 . 000563058 kg m 2 / s (toler ance 1 %). Explanation: The definition of density is M V = M 4 3 R 3 , Therefore R = bracketleftbigg 3 M 4 bracketrightbigg 1 3 = bracketleftbigg 3 (0 . 7 kg) 4 (7850 kg / m 3 ) bracketrightbigg 1 3 = 0 . 0277149 m . Using = 2 T = 2 (2 . 4 s) = 2 . 61799 s 1 and I = 2 5 M R 2 = 2 5 (0 . 7 kg)(0 . 0277149 m) 2 = 0 . 000215072 kg m 2 , we have L I = 4 M R 2 5 T = 4 (0 . 7 kg)(0 . 0277149 m) 2 5 (2 . 4 s) = . 000563058 kg m 2 / s . Question 2, chap 13, sect 4. part 1 of 1 10 points A force F x = (2 N) + (3 . 5 N) is applied to an object that is pivoted about a fixed axis aligned along the z coordinate axis. The force is applied at the point x = (4 . 1 m) +(3 . 9 m) . Find the zcomponent of the net torque. Correct answer: 6 . 55 N m (tolerance 1 %). Explanation: Basic Concept: vector = vectorr vector F Solution: From the definition of torque vector = vectorr vector F = [ x + y ] [ F x + F y ] = [(4 . 1 m) + (3 . 9 m) ] [(2 N) + (3 . 5 N) ] = [(4 . 1 m) (3 . 5 N) (3 . 9 m) (2 N)] k = (6 . 55 N m) k In this case, the net torque only has a z component. Question 3, chap 13, sect 4. part 1 of 2 10 points A particle is located at the vector position vectorr = (1 . 8 m) + (3 . 9 m) and the force acting on it is vector F = (5 . 4 N) + (1 . 6 N) . What is the magnitude of the torque about the origin? Correct answer: 18 . 18 N m (tolerance 1 %). Explanation: Basic Concept: vector = vectorr vector F Solution: Since neither position of the par ticle, nor the force acting on the particle have homework 19 FIERRO, JEFFREY Due: Apr 6 2008, 11:00 pm 2 the zcomponents, the torque acting on the particle has only zcomponent: vector = [ x F y y F x ] k = [(1 . 8 m) (1 . 6 N) (3 . 9 m) (5 . 4 N)] k = [ 18 . 18 N m] k . Question 4, chap 13, sect 4. part 2 of 2 10 points What is the magnitude of the torque about the point having coordinates [ a, b ] = [(4 m) , (6 m)]?...
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This note was uploaded on 05/11/2008 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.
 Spring '08
 Turner
 Mass, Work

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