How Long Until the Oscillator's Energy Halves?

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SUMMARY

The discussion focuses on calculating the time required for the energy of a mass-spring oscillator to reduce to half its initial value due to a frictional effect that decreases the amplitude by a factor of 0.985 per oscillation. The initial period of oscillation is 0.820 seconds. The proposed method involves using the relationship between amplitude and energy, specifically that the total energy is proportional to the square of the amplitude. The correct approach is to determine the number of oscillations needed for the amplitude to reach a level where the energy is halved, and then multiply this by the period to find the total time.

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Homework Statement


A mass M is suspended from a spring and oscillates with a period of 0.820s. Each complete oscillation results in an amplitude reduction of a factor of 0.985 due to a small velocity dependent frictional effect. Calculate the time it takes for the total energy of the oscillator to decrease to 0.500 of its initial value.


Homework Equations





The Attempt at a Solution



Tried .985^t = .5, then t = log(.5)/log(.985) but this didn't work... any other suggestions?
 
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NAkid said:
... any other suggestions?

Try a direct and simple approach, without calculus. The total E of the spring is (1/2)kA^2, where A is the amplitude. For the energy to become E/2, you can find A.

After each oscillation, it becomes cA, where c = 0.985. If it starts out with amplitude A0 and energy E0, then you can calculate after how many swings the energy becomes E0, by using the above mentioned process. Then find the time.
 

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