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Homework Help: Determining Drag Coefficient

  1. Feb 22, 2006 #1
    A fire helicopter carries a 560-kg bucket at the end of a cable 20.6 m long as in the figure below. As the helicopter flies to a fire at a constant speed of 39.2 m/s ,the cable makes an angle of 39.6 with respect to the vertical. The bucket presents a cross-sectional area of [tex]3.96m^2[/tex] in a plane perpendicular to the air moving past it. Determine the drag coefficient, assuming that the resistive force is proportional to the square of the bucket's speed.

    I've got that [tex]C_d = 2mg / (V_T)^2A\rho[/tex], but I don't know how to find the terminal velocity of the bucket to find the coefficient of drag. Can anyone help?
     

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    Last edited: Feb 22, 2006
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  3. Feb 22, 2006 #2

    NateTG

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    You don't need to use the terminal verlocity at all, but a more general expression for the force of friction. You have enough information to determine the force of friction, and you know the airspeed.
     
  4. Feb 23, 2006 #3
    But the equation for the force of friction is [tex]f_f = \mu N[/tex]. I don't know the coefficent of friction.... unless it's 1 since it's flying through the air?
     
  5. Feb 23, 2006 #4

    Pyrrhus

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    Remember Newton's 1st Law!

    [tex] \sum F_{x} = 0 [/tex]

    [tex] \sum F_{y} =0 [/tex]
     
  6. Feb 23, 2006 #5

    NateTG

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    Sorry, what I meant is that you need a more general expression for drag (rather than friction). You should be able to calculate the force that the drag exerts and work from there.
     
  7. Feb 23, 2006 #6
    What do you mean a more general equation for drag? That's all my book gives me....
     
  8. Feb 23, 2006 #7

    Pyrrhus

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    Try

    [tex] F_{drag} = \frac{C_{D}}{A} \frac{\rho v^2}{2} [/tex]
     
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