Homework 25 - sanchez (ds28677) homework 25 Turner (58220)...

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Unformatted text preview: sanchez (ds28677) homework 25 Turner (58220) 1 This print-out should have 13 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points A skater spins with an angular speed of 17 . 9 rad / s with his arms outstretched. He lowers his arms, decreasing his moment of in- ertia from 43 kg m 2 to 36 kg m 2 . a) Calculate his initial rotational kinetic energy. Correct answer: 6888 . 81 J. Explanation: Basic Concepts: L = I KE = 1 2 I 2 Given: I i = 43 kg m 2 I f = 36 kg m 2 i = 17 . 9 rad / s Solution: KE i = 1 2 I i 2 i = 1 2 (43 kg m 2 )(17 . 9 rad / s) 2 = 6888 . 81 J 002 (part 2 of 2) 10.0 points b) Calculate his final rotational kinetic en- ergy. Correct answer: 8228 . 31 J. Explanation: Solution: Angular momentum of the system is con- served, so I f f = I i i f = I i i I f KE f = 1 2 I f parenleftbigg I i i I f parenrightbigg 2 = 1 2 I 2 i 2 i I f = 1 2 (43 kg m 2 ) 2 (17 . 9 rad / s) 2 36 kg m 2 = 8228 . 31 J 003 (part 1 of 3) 10.0 points Assume: The small objects are point parti- cles. The system of nine small 6 kg objects is rotating at an angular speed of 7 rad / s. The objects are connected by light, flexible spokes that can be lengthened or shortened. x y 6 kg 6 kg 6 kg 6 kg 6 kg 6 kg 6 kg 6 kg 6 kg 7 r a d / s 8 m What is the initial angular momentum of the object? Note: An effect similar to this ocurred in the early stages of the formation of our Galaxy. As the massive cloud of dust and gas that was the source of the stars and planets contracted, an initially small angular speed increased with time. Correct answer: 24192 kg m 2 / s. Explanation: Basic Concepts: The angular momentum is L = I = ( M r 2 ) . With no external torques, angular momentum is concerved. sanchez (ds28677) homework 25 Turner (58220) 2 Let : m = 6 kg , r 1 = 8 m , r 2 = 9 m , and...
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This note was uploaded on 04/07/2011 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.

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Homework 25 - sanchez (ds28677) homework 25 Turner (58220)...

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