Solve ODE: Find Transfer Function G(S)

math111
Messages
42
Reaction score
0

Homework Statement


M\ddot{X}(t)+c\dot{X}(t)+kx(t) =f(t)
Initial Conditions:
x(0) = .02
\dot{X}(0)=0
-Use laplace transform to convert the ordinary differential equation in the time domain to an algebraic equation in the frequency domain.
-Derive the transfer Function G(S) = \frac{X(S)}{F(S)}

Homework Equations


The Attempt at a Solution


mS^{2}X(S) - .02MS + CSX(S) - .02C + KX(S) = F(S)

[mS^{2} - CS+K]X(S) = F(S) +.02MS - .02C

X(S) = F(S) +.02MS - .02C / mS^{2} - CS+K

This is where I get confused.
1. Should I of divided out the M in the beginning?(i.e. k/m, c/m..)
2. At this point do I need partial fractions to go further?
 
Last edited:
Physics news on Phys.org
math111 said:
X(S) = F(S) +.02MS - .02C / mS^{2} - CS+K
Recheck this line. You should not have any minus sign.

This is where I get confused.
1. Should I of divided out the M in the beginning?(i.e. k/m, c/m..)
2. At this point do I need partial fractions to go further?
A pity you aren't given the unknowns explicitly. Because using the quadratic formula to get the factors looks really complicated. I really don't see how to use partial fractions since you're not given F(s).
 
Defennder said:
Recheck this line. You should not have any minus sign.

A pity you aren't given the unknowns explicitly. Because using the quadratic formula to get the factors looks really complicated. I really don't see how to use partial fractions since you're not given F(s).

yeah at 3am I might make mistakes...
it should be
X(S) = [F(S) +.02MS + .02C] / [MS^2 + CS+K]

Now I see X(S) = [F(S)/M]/[S^2 + CS/M+K/M] + [.02S + .02C/M]/[S^2 + CS/M+K/M]

from here I need some more help.. I think C/M and K/M mean something else..
 
Prove $$\int\limits_0^{\sqrt2/4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx = \frac{\pi^2}{8}.$$ Let $$I = \int\limits_0^{\sqrt 2 / 4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx. \tag{1}$$ The representation integral of ##\arcsin## is $$\arcsin u = \int\limits_{0}^{1} \frac{\mathrm dt}{\sqrt{1-t^2}}, \qquad 0 \leqslant u \leqslant 1.$$ Plugging identity above into ##(1)## with ##u...
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
Back
Top