# Drag Force / Drag Coefficient

Hi

I am currently trying to work out the drag coefficient of a car, I know the formulae to work out CD, this being CD=FD/0.5xρv^2A. I can not figure out how to find FD as the formulae for this requires CD. Is there another way to find FD? The information I have is as follows:

Car Mass: 1350 kg
Rolling Resistance: 400 N
Cross Sectional Area: 2.2 m^2
Density of Air: 1.23 kg m^-3

To find CD the equation below is used

CD=FD/0.5xρv^2A

However to find FD CD is required

AN ATTEMPT AT THE SOLUTION WOULD BE

?FD?/0.5 x 1.23 kg/m^3 x 24.590 m/s^2 x 2.2

It is just the FD part I am not too sure about.

I would greatly apprecitate any help offered as I am now completely stumped.

Thanks

rock.freak667
Homework Helper
Are you given the acceleration of the car?

If you are you can apply a force balance on the car to get the value for FD.

Hi yes I am given a speed of 55mph.

rock.freak667
Homework Helper
Are you given time or distance or anything to work out the acceleration or work done by the car?

Hi

Sorry you asked for acceleration in your previous post and I gave you speed

I am not given acceleration but I am told that it is on a hill that is 3.18 degrees to the horizontal.

EDIT: Sorry I already mentioned that. It maintains a constant speed of 55mph.

rock.freak667
Homework Helper
Hi

Sorry you asked for acceleration in your previous post and I gave you speed

I am not given acceleration but I am told that it is on a hill that is 3.18 degrees to the horizontal.

EDIT: Sorry I already mentioned that. It maintains a constant speed of 55mph.

Then you should apply a force balance on the car, since it is moving at constant speed then the resultant force on the body is zero.

If you do that then you can get FD and hence CD