I know nothing about diff. equations, is this one solvable?

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Discussion Overview

The discussion revolves around the solvability of a differential equation that involves speed (v) and integrals of the function. Participants explore techniques for solving the equation, including differentiation and the use of Laplace transforms, while clarifying the nature of the equation itself.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents the equation av(t) = b - c∫v(t)^2dt - d∫v(t) and asks for a technique to solve it.
  • Another participant suggests differentiating both sides to eliminate the integral of the squared function and mentions that the resulting equation is an ODE of the "separable" kind, but cautions against using Laplace transforms due to the equation's non-linearity.
  • A different participant points out that the original equation is an integral equation rather than a differential equation.
  • A participant claims to have solved the equation by rearranging terms and integrating, but seeks clarification on the non-linearity of the equation and the limitations of the Laplace transform.
  • Another participant explains that the presence of the square of the function in one of the terms makes the equation non-linear and discusses the implications for using the Laplace transform.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the equation, with some identifying it as an integral equation and others discussing its properties as a differential equation. There is no consensus on the best approach to solve it, particularly regarding the use of Laplace transforms.

Contextual Notes

Participants note that the equation's non-linearity arises from the squared term, which affects the applicability of certain solution techniques like the Laplace transform. The discussion includes assumptions about the nature of the equation and the methods proposed for solving it.

Who May Find This Useful

This discussion may be useful for individuals interested in differential and integral equations, particularly those exploring solution techniques and the implications of non-linearity in mathematical modeling.

tamtam402
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I stumbled upon this diff. equation, which is a function of speed (v). Is there a technique I can use to solve it?

av(t) = b - c∫v(t)^2dt - d∫v(t)

Can I simply differentiate on both sides to get rid of the integral of the squared function, then use Laplace? The integrals go from 0 to an arbitrary time t.

Thanks!
 
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tamtam402 said:
Can I simply differentiate on both sides to get rid of the integral of the squared function, then use Laplace?
Yes, you can. This will transform the integral equation to an ODE. But don't use Laplace transform because the ODE is not linear.
It's an ODE of the "separable" kind, directly leading to an integral easy to solve.
Don't forget to bring back your result into the original equation (not into the ODE) in order to compute the unknown constant.
 
Last edited:
It's not a differential equation, but an integral equation (yes, they have those, too._
 
Thanks for the reply guys! I figured out how to solve it by deriving on both sides, putting the v's and dv on one side and the dt on the other side then integrating again.

I still have a question. What made the first equation non-linear? I'm not sure why Laplace cannot be used here.

Thanks!
 
tamtam402 said:
What made the first equation non-linear? I'm not sure why Laplace cannot be used here.
In one of the terms, there is the square of the sought function. As a consequence the equation is not linear.
Try to use the Laplace transform of the square of a function. It involves Laplace convolution. If you know how to cope with it, then you can use Laplace transform.
 

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