A large migratory bird has a roughly rectangular wing with an average chord c = 15 cm and span b= 1.5m. Its wing area is thus S=bx c, and the bird weighs roughly 4 kg. What is the average pressure difference Ap = P - Pu between the bird's wing lower and upper surfaces while in flight? An efficient wing typically has an average lower-to-upper pressure coefficient ACp = Cp-Cpu of between 0.5 and 1.5. This bird is quite an efficient flyer, with ACp = 1.25. Estimate the bird's flight speed at sea level. At which speed does this bird need to fly if it needs to pass above a mountain range at an altitude of 4000 m above sea level? (Use the standard atmosphere to determine density at this altitude.)