Mastering Physics: Assignment 24 Mozilla Firefox Mastering Physics: Assign... X
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Mastering Physics: Assignment 24 Mozilla Firefox Mastering Physics: Assign... X C A Turntable Has Rotation... X https:// gphys /myct/i P Most visited f FB WA WA MP R iLearn TTUMail Phys 2109-2110 Assignment 24 Item 6 Item 6 In the figure the lower disk, of mass 450 g and radius 3.1 cm is rotating at 180 rpm on a frictionless shaft of negligible radius. The pper disk, of mass 280 g and radius 2.4 cm is initially not rotating. It drops freely down onto the lower disk, and frictional forces bring the two disks to a common rotational speed. (Figure 1) Fig (a) Search the web and Windows D-61863089 Part A Find the common speed. Express your answer using two significant figures. My Answers Give Up Sub Part B Find the fraction of the initial kinetic energy lost to friction. Express your answer using two significant figures. My Answers Give Up Sub Q. Search Signed in as Emily Wiedemann Help Close Resources previous l 6 of 7 l next Continue Provide Feedback 12:08 AM 2016Explanation / Answer
moment of inertia of lower disk Il = (1/2)*ml*rl^2 = (1/2)*0.45*0.031^2 = 0.000216225 kg m^2
initial angular momentum Li = Il*wi = 0.000216225*180
after the two disk coupled
moment of inertia of upper disk = (1/2)*mu*ru^2 = (1/2)*0.28*0.024^2 = 8.064*10^-5 kgm^2
total moment of inertia If = Il + Iu
If = (0.000216225)+(8.064*10^-5) = 0.000296865 kg m^2
final angular momentum Lf = If*wf
from moentum conservation
Lf = Li
0.000296865*wf = 0.000216225*180
wf = 131.1 rpm <<<<<----------------answer
partB
initial KE , ki = (1/2)*Li^2/2Il
final KE = Kf = (1/2)*Lf^2/If
Li = Lf
fraction (Ki - Kf)/Ki = (If-Il)/If = (0.000296865-0.000216225)/0.000296865 = 0.27