Yes, this is correct. The solution to the equation for X0 is -1 / (-K - C*S).

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Discussion Overview

The discussion revolves around the formulation and solution of a differential equation related to a physical system involving a spring and damper, specifically focusing on the application of Laplace transforms. Participants are examining the correct representation of the equation and the implications of their formulations.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes that the solution for X0 is -1 / (-K - C*S) based on their manipulation of the equation.
  • Another participant challenges this by stating that terms from the differential equation and Laplace transform equation have been mixed, suggesting that the differential equation should be expressed in terms of x and δ(t) instead of including x0.
  • A subsequent reply questions the formulation of the differential equation, suggesting it should include δ(t) and correcting the signs on the right-hand side (RHS) of the equation.
  • Further clarification is sought regarding the correct representation of the forces involved, with one participant reasoning that the spring opposes the impulse while the damper acts in the same direction.
  • There is uncertainty expressed about the correct application of Laplace transforms, with a participant indicating they are new to the topic and seeking guidance on the Laplace transform of the derivative dx/dt.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as there are multiple competing views regarding the correct formulation of the differential equation and the application of Laplace transforms. The discussion remains unresolved with ongoing corrections and challenges to earlier claims.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the system, the definitions of terms used, and the steps involved in applying Laplace transforms. These aspects remain unresolved and are subject to further clarification.

MMCS
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Please see attached for problem and schematic

I know from the question i should expect a decaying exponential funtion.

Input: a unit impulse denoted in the laplace transform is 1
outputs: -Kx0 - Cdx/dt

-Kx0 - Cdx/dt +1 = 0

factorise

X0 ( -K - C*S) + 1 = 0

-1 / ( -K - C*S ) = X0

Is this correct up to now?
 

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No. You have been intermixing terms from the differential equation with terms from the LT equation. You need to start out by getting the differential equation correct. Express the differential equation in terms of x and δ(t). There shouldn't be an x0 in the differential equation, but there should be a δ(t).

Chet
 
Chestermiller said:
No. You have been intermixing terms from the differential equation with terms from the LT equation. You need to start out by getting the differential equation correct. Express the differential equation in terms of x and δ(t). There shouldn't be an x0 in the differential equation, but there should be a δ(t).

Chet

So..

δ(t) = -Kx - C(dx/dt) ?
 
MMCS said:
So..

δ(t) = -Kx - C(dx/dt) ?
There should be plus signs on the RHS. Look back at your figure. After correcting this, what is the LT of the equation?

chet
 
Chestermiller said:
There should be plus signs on the RHS. Look back at your figure. After correcting this, what is the LT of the equation?

chet

im not sure but should it be

δ(t) = -Kx + C(dx/dt)?

My reasoning is that the spring will oppose the impulse and the damper will act in the same direction?

If so, Taking laplace transforms ( I am very new to the topic )


1 = -Kx + C*S*X0(S)?
 
MMCS said:
im not sure but should it be

δ(t) = -Kx + C(dx/dt)?

My reasoning is that the spring will oppose the impulse and the damper will act in the same direction?

Vector force exerted by spring and damper on bar = (kx+c\frac{dx}{dt})(-\vec{i_x})
Vector force by impulse on bar = δ(t)(+\vec{i_x})
Sum of forces on massless bar equal to zero:
(kx+c\frac{dx}{dt})(-\vec{i_x})+δ(t)(+\vec{i_x})=0\vec{i_x}
or
-(kx+c\frac{dx}{dt})+δ(t)=0


If so, Taking laplace transforms ( I am very new to the topic )

1 = -Kx + C*S*X0(S)?
If you're learning how to use Laplace transforms, then you have to learn it right. Is this a course in Laplace transforms? According to your book, what is the Laplace transform of the function dx/dt if x = x0 at t = 0?

Chet
 

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