# Damped Oscillator Equation

1. Dec 8, 2012

the damped oscillator equation:

(m)y''(t) + (v)y'(t) +(k)y(t)=0

Show that the energy of the system given by

E=(1/2)mx'² + (1/2)kx²

satisfies:

dE/dt = -mvx'

i have gone through this several time simply differentiating the expression for E wrt and i end up with

dE/dt = x'(-vx')

im at a brick wall. Am i doing something wrong? Any help is much appreciated! Thanks

2. Dec 8, 2012

I have also assumed that y and x are interchangeable variables here, as no other information has been provided

3. Dec 8, 2012

### Mute

I don't see anything wrong with your calculation. In fact, double check the units for your expressions - I don't think the suggested answer "$m\gamma \dot{x}$" even has the same units as $dE/dt$.

4. Dec 9, 2012

### pasmith

That must be wrong: it requires that $E = C - mvx$ for some constant C, which is not the case.

That is the right expression for dE/dt.