We read the source code.
m = mass of penguin = 5 kg
g = acceleration due to gravity = 9.8 m/s^2
ρ = density of air = 1.225 kg/m^3
A = cross-sectional area = 0.1 m^2
C_d = drag coefficient = 0.8
Plugging in the values:
v_t = √((2 × 5 kg × 9.8 m/s^2) / (1.225 kg/m^3 × 0.1 m^2 × 0.8))
v_t = √(98 / 0.98)
v_t = √100
v_t = 10 m/s Therefore, the terminal velocity of an average-sized penguin falling head-first is approximately 10 m/s or 36 km/h.1345