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Homework Help: Projectile motion but with resistive force

  1. Sep 4, 2005 #1
    I have this question:

    A 10kg projectile is launched with an initial speed of 100m/s at an elevation of 35 degrees. The resistive force is R = -bv , where b =10kg/s.

    Determine the horizontal and vertical component coordinates of the projectile as functions of time.

    How do I do this?? I urgently need the complete solution to this! Thanx!
  2. jcsd
  3. Sep 4, 2005 #2


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    Gold Member

    Basically you're looking for a differential equation for the x-component of the velocity. This is not difficult to find because you can work with this component without thinking about the y-component. You know that [itex]\vec{R}=-b\vec{v}[/itex], so then [itex]R_x=-bv_x[/itex]. You also know that [itex]\vec{F}=\vec{R}=m\vec{a}=m\vec{\dot{v}}[/itex], so [itex]R_x=m\dot{v_x}[/itex]. Substitute for R. Do you recognize the solution of the differential equation you get?
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