# Homework Help: Air resistance co-efficient

1. Jan 28, 2012

### luigihs

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. Jan 28, 2012

### physicsisgrea

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 ?

3. Jan 28, 2012

### luigihs

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 ?

4. Jan 28, 2012

### physicsisgrea

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.

5. Jan 28, 2012

### luigihs

Where do you get that number sorry Im confused! :(

6. Jan 28, 2012

### physicsisgrea

put m = mass of the object
put g = 9.8 m/s^2
put v = terminal velocity