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Modeling with Differential Equations

  1. Jan 21, 2013 #1
    1. The problem statement, all variables and given/known data

    A falling body of mass m, encounters air resistance proportional to its instantaneous velocity, v. Use Newton's second law to find the DE for the velocity, v at time, t.

    2. Relevant equations
    I've been reading this section quite a bit and am still not getting it! I'd appreciate a simple breakdown of this problem.


    3. The attempt at a solution

    I know Newton's second law is F=ma, and a=[itex]\frac{dv}{dt}[/itex]= -g, in this problem. I've checked the answer in the back of the book to see if I can work it backwards and then maybe get an idea of whats going on, but I don't think I've dealt with air resistance, k, in any problems before. Even in my physics class.
     
  2. jcsd
  3. Jan 21, 2013 #2

    SammyS

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    Newton's 2nd Law: The net force on a body of mass, m, is given by Fnet = ma .

    For this problem Fnet = mg - kv , and is in the downward direction.
     
  4. Jan 22, 2013 #3
    I see. There was an image next to the question with those being opposite. Now to put ity into a differential equation form? I was watching a video about differential equations and there being a 1st ODE format using p(x) and q(x)?
     
  5. Jan 22, 2013 #4

    haruspex

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    What differential equation relates acceleration to velocity?
     
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