Simple Harmonic Motion - what is its new period

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SUMMARY

The discussion focuses on calculating the new period of oscillation for a meter stick after it is sawed to a length of 0.76 m. Initially, the period is 5 seconds for a 1 m stick, using the formula T = 2π√(I/k). The moment of inertia (I) is calculated as I = 1/12 mL². The user attempts to find the new period but encounters errors, suggesting the need to apply the parallel axis theorem for the moment of inertia. Ultimately, the correct period is determined to be approximately 3.31 seconds after considering the mass reduction and height factors.

PREREQUISITES
  • Understanding of Simple Harmonic Motion (SHM)
  • Familiarity with the moment of inertia (I) calculations
  • Knowledge of the parallel axis theorem
  • Basic proficiency in oscillation period formulas
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  • Study the derivation and application of the moment of inertia for different shapes
  • Learn about the parallel axis theorem and its implications in rotational dynamics
  • Explore the effects of mass distribution on oscillation periods
  • Investigate the relationship between length and period in Simple Harmonic Motion
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Physics students, educators, and anyone interested in the principles of oscillation and rotational dynamics will benefit from this discussion.

mattmannmf
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A uniform meter stick is hung at its center from a thin wire. It is twisted and oscillates with a period of 5 s. The meter stick is then sawed off to a length of 0.76 m, rebalanced at its center, and set into oscillation.

what is its new period
I= 1/12 mL^2

equation: T= 2 pi * sqrt (I/k)
where T= 5
L= 1

I solved for K in terms of m (mass)...where i got k=7.599 m

then i replugged it into the same equation but where
T= unknown (trying to find)
L=.76

the mass cancels out and my answer gives me 3.8... which is wrong when i checked.

The only thing i can see is that I am using the wrong "I" for using the same equation 2nd time when i replugged it in. Should i be using the parallel axis theorem where

I= 1/12 mL^2 + Md^2
(since its not revolving around its center of mass)
L=1
d= .76

when i tried that i got my answer to be 6.28...wrong again
 

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The eqn for I for a rectangular plate is m(l^2+h^2)/12 where l and h are length and height respectively. It is revolving about the center of mass in both cases so no need for parallel axis theorum. You may need to solve for height, if the factor 0.76^3 isn't giving the right answer (remember the mass is being reduced by 24% as well).

BTW, neglecting the height, I got an answer of T=3.31s
 
Last edited:

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