# hw28 - homework 28 Turner(58185 This print-out should have...

This preview shows pages 1–2. Sign up to view the full content.

This print-out should have 13 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 (part 1 oF 2) 10.0 points A skater spins with an angular speed oF 17 . 4 rad / s with his arms outstretched. He lowers his arms, decreasing his moment oF in- ertia From 43 kg · m 2 to 37 kg · m 2 . a) Calculate his initial rotational kinetic energy. Correct answer: 6509 . 34 J. Explanation: Basic Concepts: L = KE = 1 2 2 Given: I i = 43 kg · m 2 I f = 37 kg · m 2 ω i = 17 . 4 rad / s Solution: KE i = 1 2 I i ω 2 i = 1 2 (43 kg · m 2 )(17 . 4 rad / s) 2 = 6509 . 34 J 002 (part 2 oF 2) 10.0 points b) Calculate his fnal rotational kinetic en- ergy. Correct answer: 7564 . 91 J. Explanation: Solution: Angular momentum oF the system is con- served, so I f ω f = I i ω i ω f = I i ω i I f KE f = 1 2 I f p I i ω i I f P 2 = 1 2 I 2 i ω 2 i I f = 1 2 (43 kg · m 2 ) 2 (17 . 4 rad / s) 2 37 kg · m 2 = 7564 . 91 J 003 (part 1 oF 3) 10.0 points Assume: The small objects are point parti- cles. The system oF fve small 2 kg objects is rotating at an angular speed oF 3 rad / s. The objects are connected by light, ±exible spokes that can be lengthened or shortened. x y 2 kg 2 kg 2 kg 2 kg 2 kg 3 r a d / s m What is the initial angular momentum oF the object? Note: An e²ect 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: 270 kg m 2 / s. Explanation: Basic Concepts: The angular momentum is L = I ω = ( M r 2 ) ω . With no external torques, angular momentum is concerved. Let : m = 2 kg , r 1 = 3 m , r 2 = 7 m , and ω 1 = 3 rad / s .

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 05/02/2009 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas.

### Page1 / 5

hw28 - homework 28 Turner(58185 This print-out should have...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online