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Homework Help: Air resistance co-efficient

  1. Jan 28, 2012 #1
    1. Calculate the air resistance co-efficient of the ballon


    I trying to do my best because I have this equations in my notes Fd = k . v^2 and its says the force of air resistance is proportional to the square of the velocity of the object.

    So I only now v^2 I think is my terminal velocity that is 2.9584 , but I dont know K because is the air resistance coefficient, and I dont know the force drag ( Fd)

    NOW I have this other equation For an object with mass m and air resistance coefficient k the terminal velocity is given by:

    Vt = √(m.g/k)

    and this I know Vt is 2.9584 , m is 2.3192g , and g is 9.8 but the only thing I dont know is K because is the air coefficient , and I can rearrange the equation like k = √(m.g/vT) ... but I not sure please help me out guys.
     
  2. jcsd
  3. Jan 28, 2012 #2
    If you have to find "k":

    mg = kv^2, when the object is in terminal velocity.
    Rearrange we have mg/v^2 = k.

    m = 2.3192 grams or 2.3192 x g ?

    What is your problem actually?
     
  4. Jan 28, 2012 #3
    mg/v^2 = k

    Ok so the balloon mass is 2.3192 grams , g = 9.8 m/s^2 right? , and v is that my terminal velocity or what velocity do I have to put ?
     
  5. Jan 28, 2012 #4
    If you have find k, based on your equation "air drag = k times v^2",
    k = mg/v^2 = 0.002596871681

    Assume v is in m/s

    Plug in the terminal velocity cause "air drag equals to mg" when it has the terminal velocity.
     
  6. Jan 28, 2012 #5
    Where do you get that number sorry Im confused! :(
     
  7. Jan 28, 2012 #6
    put m = mass of the object
    put g = 9.8 m/s^2
    put v = terminal velocity
     
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