Could you help me solve first order diff eq?

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  • Thread starter Thread starter hangainlover
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    Diff eq First order
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Discussion Overview

The discussion revolves around solving a first-order differential equation of the form dv/dt = g - (k/m)v^2. Participants explore various techniques for solving this equation, including separation of variables and integration methods.

Discussion Character

  • Exploratory, Technical explanation, Mathematical reasoning

Main Points Raised

  • One participant presents the differential equation and expresses difficulty in finding a solution method.
  • Another participant suggests that the initial approach may be correct but hints at possible calculation errors.
  • A third participant encourages the use of standard integrals from a library to assist in solving the equation.
  • Separation of variables is proposed as a viable method, with a suggestion to transform the integral into a known form.
  • A later reply discusses factoring the expression g - (k/m)v^2 as a difference of squares, indicating that this could facilitate integration using partial fractions.

Areas of Agreement / Disagreement

Participants express varying levels of confidence in the initial approach, with some suggesting alternative methods without reaching a consensus on the best solution strategy.

Contextual Notes

Some assumptions about the integrals and the specific forms of the functions involved may not be fully articulated, and there is a reliance on external resources for standard integrals.

hangainlover
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dv/dt=g-(k/m)*v^2
i thought about all sorts of diff eq solving techniques
but nothing comes up to my mind

dv/(g-(k/m)*v^2)=dt
but it doesn't really help ...
 
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I think it's quite correct, but there could be some errors in calculation..anyway:

http://spiro.fisica.unipd.it/~mimo/altro/sol.JPG
 
Last edited by a moderator:
hi hangainlover! :smile:

(try using the X2 tag just above the Reply box :wink:)

learn your list of standard integrals from the pf library :wink:
 
Separation of variables seems to work. Just try to transform the integral [tex]\int \frac{1}{g-\frac{k}{m}v^2}dv[/tex] to the case xxvi of the standard integrals link provided by tiny-tim.
 
Specifically,
[tex]g- \frac{k}{m}v^2[/tex]
, being a "difference of squares", factors as
[tex](\sqrt{g}- \sqrt{k/m}v)(\sqrt{g}+ \sqrt{k/m}v)[/tex]
and so that function can be integrated by "partial fractions".
 

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