# Damped Mass Spring System

1. Apr 26, 2012

### FHamster

So the equation is x'' + 10x' + 64x = 0
x(0) = 1
x'(0) = 0
I get general solution of e^(-5t)(c1*cos(6.245t) + c2sin(6.245t) )
From there I get e^(-5t)cos(6.245t)+5e^(-5t)sin(6.245t)
but it wrong. What the gerbils am I doing wrong?

Thanks

2. Apr 26, 2012

### tiny-tim

Welcome to PF!

Hi FHamster! Welcome to PF!

(try using the X2 button just above the Reply box )
(do hamsters not like gerbils? )

erm … haven't you left out a 6.245 ?

3. Apr 26, 2012

### HallsofIvy

If $y= e^{5t}(c_1cos(6.245t)+ c_2sin(6.245t))$
then $y(0)= e^0 (c_1 cos(0)+ c_2 sin(0))= c_1= 1$ so you have that coefficient right.

$$y'= 5e^{5t}(c_1 cos(6.245t)+ c_2 sin(6.245t))+ e^{5t}(-6.245 sin(6.245 t)+6.245cos(6.245t))$$

$$y'(0)= 5e^0(c_1 cos(0)+ c_2 sin(0))+ e^0(-6.245c_1 sin(0)+ 6.245c_2 cos(0))$$
$$y'(0)= 5(c_1)+ (1)(6.245c_2)= 11.245$$
Knowing that $c_1= 1$, solve for $c_2$.

4. Apr 29, 2012

### FHamster

Re: Welcome to PF!

Thanks, following some of these guidelines and doing some recalcumacations. I managed to get it right

Hamsters are the masterrace.