Physics Help Forum Determine the natural frequency 2

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 Feb 25th 2017, 03:10 PM #1 Junior Member   Join Date: Feb 2017 Posts: 2 Determine the natural frequency 2 The question is: Determine the natural frequency of the rotor shown below given the following data: Moment of inertia of rotor Jr=0.6 kgm^2 Diameter of shaft d=38.0mm Length of shaft L=189.0 mm Material of shaft Steel Modulus of Rigidity 82 GPa My solution is: I=(π*d^4)/64=(π*0.038^4)/64=102e-9 ω=((J*G)/(I*L))^0.5=((0.6*82e9)/(102e-9*0.189))^0.5=1.598e9 F=1.598e9/2π=0.254e9 The correct answer should be 61.2 what am I doing wrong? Attached Thumbnails
 Mar 8th 2017, 10:57 AM #2 Senior Member   Join Date: Jul 2009 Location: Kathu Posts: 114 Determine the natural frequency 2 J=PI()/32*(38*10^-3)^4= 2.04708E-07 m^4 G = 82000000000 GPa L = 0.189 m I = 0.6 kg * m^2 ω=((J*G)/(I*L))^0.5 = 384.740176 Rads / sec F = W / (2*pi) = 61.23 Hz

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