Early test flights for the space shuttle used a glider

[kritzy]

Homework Statement

Early test flights for the space shuttle used a "glider" (mass of 940 kg including pilot). After a horizontal launch at 470 km/h at a height of 4000 m, the glider eventually landed at a speed of 210 km/h . What would its landing speed have been in the absence of air resistance(in km/h)? What was the average force of air resistance exerted on it if it came in at a constant glide angle of 15 degrees to the Earth's surface?

Homework Equations

Ki + Ui = Kf + Uf
.5mv$$^{2}$$+mgh=.5mv$$^{2}$$

The Attempt at a Solution

I'm not so sure about the second question but here's what I did for the first one.
I changed the units so that the answer would be in km/h.
g=35.28 km/h
h=4 km
v$$^{2}$$=[2(.5mv$$^{2}$$+mgh)]/m
v$$^{2}$$=[2(.5(940)(470)$$^{2}$$+(940)(35.28)(4)]=221182.24
v=470km/h
Unfortunately, this answer is incorrect. Any help would be greatly appreciated.

 

[Phrak]

g is acceleration? The units could be kilometers per hour squared, rather than kilometers per hour.

 

[rl.bhat]

In the absence of air resistance, the horizontal velocity will remain as it is.
Find its velocity when if falls through 4 km. The resultant of this velocity and the horizontal velocity will give the landing velocity.

 

[kritzy]

Thanks. I got the first part. As for the second question, I'm not quite sure how to go about it. I think I'm suppose to use F=ma. So I caculated the acceleration.
a=(v$$^{2}$$-v$$^{2}_{0}$$)/(2x)
a=(210$$^{2}$$-470$$^{2}$$)/((2)(4))=-22100

F=ma=(940)(-22100)=-2077400

But that only gets me the force of the gilder and doesn't include friction. I was also thinking that I should get the sum of forces.So
F$$_{gilder}$$-F$$_{friction}$$=ma
I don't think that's quite right either. There suppose to be a 15 degree angle but I don't know where it goes. Can somebody help me?