# Entropy and damping osscilations

1. Nov 17, 2005

### ilovephysics

i just have 2 questions i want to clear up so i can understand the concepts more, thanks

1) if you are calculation entropy change from path a to b and the path is isobaric (cont. pressure) how do you do it? the formula for entropy change is dQ/T, but i am unsure about what T to use, also i cannot use mclnT2/T1 because i do not know the mass of the gas, how should i solve a problem like this?

2) if you are given the mass of an object and spring const., initial amplitude and info that the amplitude is 3/4 of what it was initially in 4 cycles, how do you calculate b, we dont know the period but do we use w^2=k/m? the question, being about damped ossilators throws me off a bit and im unsure how to start a problem like this

2. Nov 17, 2005

### Physics Monkey

Regarding question 1, I assume we are talking ideal gas here? In order to calculate the change in entropy you need to integrate dS from the initial to the final temperature. Can you find a way to relate dQ to dT? Hint: think about the heat capacity for constant pressure processes.

Regarding question 2, you know how long it takes to execute each cycle, right? Try setting up an equation that tells you that $$x(4T) = \frac{3}{4} x(0)$$. Where $$T$$ is the "period" of the system (though the system isn't actually periodic, this is simply the period of the periodic part).

3. Nov 18, 2005

### ilovephysics

yes it is a monoatomic ideal gas, when we integrade dS we get mCvln(t2/t1) dont we? i am unsure where to go from there because we do not know the mass

for question 2, we are not given the time it takes to complete each cycle, we are given mass, spring const, initial A, A after 4 cycles, and the equation F=-bv, when i did this question i just used w^2=k/m and found the period that way but im pretty sure that isn't correct since its about a damped osscilator