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Homework Help: Position Dependent

  1. Dec 12, 2008 #1
    A particle moving along the x-axis is acted upon by a resisting force which is such that at a time t for it to travel a distance x is given by t=Ax^2+Bx+C, where A, B, and C are constants. show that the magnitude of the resisting force is proportional to the cube of the instantaneous speed.

    I know the chain rule needs to be used and it is just a calculus problem, but I can't seem to start it.
    Last edited: Dec 12, 2008
  2. jcsd
  3. Dec 13, 2008 #2
    Start by writing down [itex]dt /dx = \cdots[/itex]
  4. Dec 13, 2008 #3
    dt/dx= 2Ax+Bx

    Now I know I need to get velocity, which is dx/dt, but the only way I can see is to multiply the above by dx/dt, and I don't know if that is right. What about the distance x? Where does it come in?
  5. Dec 13, 2008 #4


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    [tex]\frac{dx}{dt} = \frac{1}{\left(dt/dx\right)}[/tex]

    You might also want to recheck your derivative.
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