When testing a new car, the car drives with a constant speed v = 140 km/h. The
power of car’s engine is P = 120 kW and we know that 80% of this power is con-
verted to movement. Determine the drag coefficient in air if the cross section of the
car has circular shape, its value is S = 3 m2
, and air can be described as a liquid
with viscosity η = 2,2 · 10−3 Ns/m2 and density ρ = 1,2 kg/m3
. Calculate the
Reynolds number and determine if the linear or quadratic drag equation is valid in
this case or neither of them.