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Computing distance and time from a differential equation

  1. Aug 5, 2011 #1

    having given 2 speeds v1 and v2 and the equation: k1*v'=k2-k3*v[itex]^{2}[/itex] how do i compute the distance traveled from v1 reaching v2 and the time needed. (k1,k2,k3 are constants).

    i think i have to integrate to find the distance, but i just can't figure quite how to do it.

    any tips are greatly appreciated.
  2. jcsd
  3. Aug 5, 2011 #2
    You need to find a function for velocity v(t). You can integrate v(t) to find the distance. To obtain this function, you can solve your differential equation using separation of variables:

    [itex]k_{1}\frac{dv}{dt}=k_{2}-k_{3}v^{2} \implies k_{1}\frac{dv}{k_{2}-k_{3}v^{2}} = dt[/itex]
  4. Aug 5, 2011 #3


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    And you can use "partial fractions" to integrate that: [itex]k_1- k_2v^2= \left(\sqrt{k_1}- \sqrt{k_2}v\right)\left(\sqrt{k_1}+ \sqrt{k_2}\right)[/itex]
  5. Aug 5, 2011 #4
    thanks for that, i managed to figure out the integral but sadly it does not converge given the constants that i have.
    thanks again
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