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Metal disk problem! 
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#1
Nov2912, 12:32 PM

P: 326

1. The problem statement, all variables and given/known data
A uniform metal disk (M = 8.21 kg, R = 1.88 m) is free to oscillate as a physical pendulum about an axis through the edge. Find T, the period for small oscillations. 2. Relevant equations [itex]I = mr^{2}/4[/itex] [itex]T = 2\pi √(I/mgd)[/itex] 3. The attempt at a solution I combined the formula together to get: [itex]T = 2\pi √((mr^{2}/4)/(mgr))[/itex] [itex]T = 2\pi √(r/(4g))[/itex] But the answer is incorrect 


#3
Nov2912, 01:56 PM

P: 326




#4
Nov2912, 02:15 PM

Mentor
P: 41,555

Metal disk problem!



#5
Nov2912, 06:29 PM

P: 326

I am not sure which path to go for... 


#7
Nov2912, 07:01 PM

P: 326

[itex]I = I_{center} + md^{2}[/itex] [itex]I = mr^{2}/2 + mr^{2}[/itex] [Since the disk rotates about an axis through the edge, we must add the inertia by mrČ. r is the distance between the center and the edge of the disk.] [itex]I = 3mr^{2}/2[/itex] Is that how I approach this? Let me know where I go wrong. Otherwise, I can just plug and chug this expression: [itex]T = 2\pi √((3mr^{2}/2)/(mgr))[/itex] [itex]T = 2\pi √(3r/(g))[/itex] 


#8
Nov2912, 07:18 PM

P: 326

Nvm. My answer is right. Thanks for your help by the way!



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