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July 30, 2014

Homework Help: Re: Physics/Math

Posted by COFFEE on Saturday, February 10, 2007 at 10:15pm.

Calculate the ratio of the drag force on a passenger jet flying with a speed of 750 km/h at an altitude of 10 km to the drag force on a prop-driven transport flying at one-fifth the speed and half the altitude of the jet. At 10 km the density of air is 0.38 kg/m3 and at 5.0 km it is 0.67 kg/m3. Assume that the airplanes have the same effective cross-sectional area and the same drag coefficient C.
(drag on jet / drag on transport.

Please help :)

* Physics/Math - bobpursley, Saturday, February 10, 2007 at 7:13pm

You must have been given some equations for drag force, these equations vary, but typically they depend on Area, a coefficeint, and velocity^2.

Post your equations and work, and I will critique.

* Physics/Math - COFFEE, Saturday, February 10, 2007 at 9:54pm

Sorry, the equation given is:

D=1/2(Dp)(Area)(Velocity^2)

I do not understand what area I am trying to calculate and what the constant equals. How do I find Dp and Area???

You dont need area. Dp is density.
You are calcualting the ratio of drag for th jet as compared to the prop plane.

Forcejet/forceprop=densityjetair*vj^2 /densityprop*vp^2

Notice all the units divide out. The donstant is notshowing, but it divides out anyway.

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