Damped Oscillatory motion : Period

[Bedeirnur]

Relevant equations
1)

2) $$T = \sqrt{ \frac{m}{k} }$$
3) $$T = \frac{2 \pi }{ \omega }$$In some problems about damped oscillatory motion, the requests ask for example "Calculate the amplitude after 20 oscillations"

I know that i need to find the period first of all but :

Do i find the period by using equation number 2? Is that constant? I've seen other threads where they calculated T with (2) and used it for everything but, if we have a different value of \omega overtime, why did we use the initial \omega to find the period?

If i divide 2π by

what do I find? Isn't that the period?

 

[Spinnor]

Maybe b^2/4m^2 is small compared to k/m? If you are given b^2/4m^2 just use it in your equation (1).

See,

https://www.google.com/search?q=Dam...yuGwBOGDgsgF&ved=0CAcQ_AUoAQ&biw=1360&bih=649

From the above,

http://www.bog5.in.ua/lection/vibration_lect/lect4_vibr_eng.html

About a 1/4 down the page.