Why do Olympic downhill skiers tuck?

Why do Olympic downhill skiers tuck? Find the terminal speeds for an 80 kg skier going down a 40° snow covered slope on skis standing straight up and in a racer's tuck. Both friction and aerodynamic drag are important. Model the skier as a cylinder that is 1.8 m tall and 0.4 m wide; see the figures on the screen which also give the appropriate drag coefficients. The coefficient of kinetic friction between the skis and the snow is 0.06 and the density of air is 1.2 kg/m3.

What is the terminal velocity when the skier is (a) standing and (b) in a racing tuck? 

With freebody digram pls.