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Projectiles with DE's

  1. May 16, 2006 #1
    I this how you would describe projectile motion in terms of DE's?

    [tex]\frac{dy}{dt} = 25.0 - gt[/tex]
    [tex]\frac{dx}{dt} = 10.0[/tex]
     
    Last edited: May 16, 2006
  2. jcsd
  3. May 16, 2006 #2

    arildno

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    No. For one, "g" doesn't equal 9.8 in most common choices of units.
     
  4. May 16, 2006 #3
    Ok, well I changed it to "g". What else is wrong?
     
    Last edited: May 16, 2006
  5. May 16, 2006 #4

    dav2008

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    Well if your initial velocities (25 and 10) are given in m/s then there's no problem of using 9.8 for g.
     
  6. May 16, 2006 #5
    That's what I intended.
     
  7. May 16, 2006 #6

    arildno

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    Consider your actual question. Nowhere did you state what 25.0 or 10.0 represent, and you wanted an answer for a GENERAL description of projectile motion in terms of D.E.
    Thus, you ought to have written something like:

    [tex]\frac{dy}{dt} = v_{0,y} - gt[/tex]
    [tex]\frac{dx}{dt} = v_{0,x}[/tex]
    where x(t), y(t) are horizontal and vertical positions as functions of time t, [itex]\vec{v}_{0}=(v_{0,x},v_{0,y})[/itex] is the initial velocity, and "g" is the acceleration due to gravity.

    If you had written it as that, your equations would have been proper to your question.
     
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