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Particle motion ode (1st order nonlinear nonhomog)

  1. Jul 10, 2012 #1
    hi all,

    I've been trying to work this problem out,

    [itex]\frac{dv}{dt}-A(B-v)^{1.6}=G [/itex]

    A, B and G are constants

    and Matlab can't give me a solution either. I'm wondering if there is even a solution?
     
  2. jcsd
  3. Jul 10, 2012 #2
    Hi,

    Just realised I can make an assumption for B = 0. Does this make it solvable?
     
  4. Jul 11, 2012 #3
    Hi !
    The ODe is of the "separables variables" kind (see in attachment) :
     

    Attached Files:

  5. Jul 11, 2012 #4
    wow! thanks
     
  6. Jul 11, 2012 #5
    Sorry, there was a typo at the end of the attached page :
     

    Attached Files:

  7. Jul 11, 2012 #6
    Since v represents velocity, can I then integrate the v-equation? Are inv. Beta functions integratable?

    Or would it be simpler to determine the x-position by setting up the original equation as a second order derivative as:

    d2xdt2−A(B−v)^1.6=G

    and as B = 0 then

    [itex]\frac{d^2x}{dt^2}+A(\frac{dx}{dt})^{1.6}=G[/itex]
    with initial conditions
    dx/dt(0) = 0

    i.e. particle initially at rest

    Sorry to ask again, but could you show me this solution? I really struggle with maths.
     
    Last edited: Jul 11, 2012
  8. Jul 12, 2012 #7
    Hi !

    If B=0 your basic equation dv/dt−A(−v)^1.6=G implies v<0 or v=0. If not, (-v)^1.6 would not be real and the solution v(t) would not be real, which is not correct on a physical point of view. So v<0 or v=0.
    In the general solution given in my preceeding post, let c=0 and B=0 in the formula. Then Y(0)=0 ; Inverse Beta (0) = 0 which leads to v=0.
    The expected solution with condition v=0 at t=0 is obtained with c=0 in the formula.

    The function v(t) is not a simple Inverse Beta function, but a combination of several functions with the Inverse Beta among them. It's far too complicated for formal integration. I think that the only practical way is numerical integration. If it is that what you want, the simplest way is probably to use a numerical process for solving directly the differential equation.
     
    Last edited: Jul 12, 2012
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