
#1
Jun610, 04:57 PM

P: 62

1. The problem statement, all variables and given/known data
Note this is exam revision rather than actual course work worth marks, so there is no need to be deliberately vague :) The question comes in two parts, regarding a lightly damped harmonic oscillator with frequency 10 kHz and an amplitude that decays by 25% over 300 oscillations. First I am asked to calculate the logarithmic decrement, and then to make an expression that allows the amplitude to be calculated as a function of time elapsed. 2. Relevant equations δ=(1/N)ln(A_{0}/A_{N}) 3. The attempt at a solution The log decrement is 9.59x10^{4}. Easy. For the second part, simply rearranging the log decrement formula gives A_{N}=A_{0}e^{Nδ}. Knowing that N = 10,000*t, I get A(t)=A_{0}e^{9.59t}. What I do not understand is why my course notes give A(t)=e^{9.59t}. Why is this answer not multiplied by A_{0}? Mathematically and physically, this does not make sense to me  the amplitude as a function of time definitely does depend on the initial amplitude! Am I right in thinking that is a mistake? Thanks! 



#2
Jun610, 05:04 PM

HW Helper
P: 2,156

Yes, you're right. If nothing else, the units don't match, that tells you the formula in your notes can't be correct.




#3
Jun710, 02:09 AM

P: 62

Ah good, thanks for confirming that!



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