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4. Aerodynamic drag on humans is not usually important, but it does influence sprinters, swimmers, cyclists, etc. Consider a simple model of a human in the form of a smooth spherical head on top of a smooth cylindrical torso (trunk or main part of human body) on two smooth cylindrical legs. The arms are neglected. Assume a head diameter of 0.2m, 0.3m diameter and 0.7m length for the torso and 0.1m diameter and 0.8m length for the legs. a) Find the drag force when this simple model of a human is running in stationary air at 15 km/h, and calculate the power required to overcome this drag. For air take the density to be 1.23 kg/m³ and the kinematic viscosity to be 1.5 x 10-5 m²/s. [9 marks] b) Calculate the drag force and the power required to overcome this drag when this simple model of a human is running at 15 km/h i) against a wind of 5 km/h, opposing the direction of motion [4 marks] ii) with a wind of 5 km/h behind, in the direction of motion. [4 marks] As for part a), the air density is 1.23 kg/m³ and the air kinematic viscosity is 1.5 x 10-5 m²/s. Provide an explanation for the variations observed in the calculated drag force and power in parts a) and b). [8 marks]