Differential equations - transforming from one to another

Basheesh
Messages
4
Reaction score
0

Homework Statement



<br /> m\frac{d^{2}x}{dt^{2}}+c\frac{dx}{dt}+kx=F_{0}cos\omega t\\<br /> LC\frac{d^{2}V_{c}}{dt^{2}}+RC\frac{dV_{c}}{dt}+V_{c}=V_{0}cos\omega t<br />These two equations are for two different physical phenomena. The first is for a mass moving along an x axis. The mass is affected by a springforce k, a dampener with constant c and an outer force F(t), here set to F_0cost(\omega t).
Explanation of the second equation follows. The gist is that they are mathematically the same (I'm translating from danish, let me know if you need the rest).

a) show that both differential equations can be brought to the form:

1:
<br /> \frac{dx^{2}}{dt^{2}}+2\alpha \frac{dx}{dt}+\omega_{0}^{2}x=fcos\omega t<br />

Where \alpha \geq 0 and we assume \omega &gt; 0

Homework Equations



1:
<br /> m\frac{d^{2}x}{dt^{2}}+c\frac{dx}{dt}+kx=F_{0}cos\omega t, LC\frac{d^{2}V_{c}}{dt^{2}}+RC\frac{dV_{c}}{dt}+V_{c}=V_{0}cos\omega t<br />2:
<br /> \frac{dx^{2}}{dt^{2}}+2\alpha \frac{dx}{dt}+\omega_{0}^{2}x=fcos\omega t<br />

The Attempt at a Solution



I'm not even sure where to start with this.
So I'm thinking that I somehow need to use:
<br /> \omega_{0}^{2} = c^2 + 4mk<br />

and possible take the integral of the whole thing. But I am pretty lost.
 
Last edited:
Physics news on Phys.org
which question are you having trouble? 1 or 2?
 
I'm having trouble with a) for now. I edited out b to avoid confusion. But I might add it later, as I think I might have trouble with that one too.
 
Use, x=Ae^{kt}+Be^{-kt} to find the general solution and to find the particular integral x=C\cos\omega t+D\sin\omega t.
 
But how does that help me writing the two equations in the form of (1)?
 
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