This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: lew (dl9564) – hk4 – Opyrchal – (41104) 1 This printout should have 8 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A constant torque of 23 . 5 N · m is applied to a grindstone for which the moment of inertia is 0 . 165 kg · m 2 . Find the angular speed after the grindstone has made 17 rev. Assume the grindstone starts from rest. Correct answer: 174 . 43 rad / s. Explanation: Let : τ = 23 . 5 N · m , I = 0 . 165 kg · m 2 , and N = 17 rev . summationdisplay vector τ ext = d vector L dt For constant torque the angle of rotation of the grindstone is defined by τ = Iα α = τ I = d 2 θ dt 2 , and θ = N 2 π where N is the number of revolutions. Thus ω 2 = 2 αθ ω = √ 2 αθ = radicalbigg 2 parenleftBig τ I parenrightBig (2 π N ) = radicalbigg 4 π τ N I = radicalBigg 4 π (23 . 5 N · m) (17 rev) . 165 kg · m 2 = 174 . 43 rad / s . 002 10.0 points The top in the figure has a moment of inertia of 0 . 0003 kg · m 2 and is initially at rest. It is free to rotate about a stationary axis AA ′ . A string, wrapped around a peg along the axis of the top, is pulled in such a manner as to maintain a constant tension of 5 . 11 N in the string. b 5 . 11 N A A ′ If the string does not slip while wound around the peg, what is the angular speed of the top after 89 cm of string has been pulled off the peg? Correct answer: 174 . 124 rad / s. Explanation: Given : I = 0 . 0003 kg · m 2 , F = 5 . 11 N , ω = 0 , and s = 89 cm = 0 . 89 m . W net = K F K i = 1 2 I ω f 2 F s = 1 2 I ω f 2 ω f 2 = 2 F s I ω f = radicalbigg 2 F s I = radicalBigg 2 (5 . 11 N) (0 . 89 m) . 0003 kg · m 2 = 174 . 124 rad / s . 003 10.0 points lew (dl9564) – hk4 – Opyrchal – (41104) 2 An Atwood machine is constructed using a disk of mass 2 kg and radius 24 . 6 cm....
View
Full
Document
This note was uploaded on 01/22/2009 for the course PHYS Phys 106 taught by Professor Opyrachal during the Fall '08 term at NJIT.
 Fall '08
 opyrachal

Click to edit the document details