HW4 Solution

HW4 Solution - lew (dl9564) – hk4 – Opyrchal –...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

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

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: lew (dl9564) – hk4 – Opyrchal – (41104) 1 This print-out should have 8 questions. Multiple-choice 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.

Page1 / 5

HW4 Solution - lew (dl9564) – hk4 – Opyrchal –...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online