Answer
a). Friction force opposes the relative motion between the feet and the surface. So, if the friction force will not act, the foot will slip and perform a relative motion to the surface.
b). Depending on the direction of the flow of the wind, the wind will either increase or decrease the air resistance.
In first case, suppose if the wind is blowing opposite to the direction of the motion, it will increase the air resistance as the vehicle will have to perform more work to overcome air resistance as well as opposition of the wind.
If the wind flows in the direction of motion of vehicle, the air resistance decreases.
Work Step by Step
a). Friction force opposes the relative motion between the feet and the surface. So, if the friction force will not act, the foot will slip and perform a relative motion to the surface.
b). Depending on the direction of the flow of the wind, the wind will either increase or decrease the air resistance.
In first case, suppose if the wind is blowing opposite to the direction of the motion, it will increase the air resistance as the vehicle will have to perform more work to overcome air resistance as well as opposition of the wind.
If the wind flows in the direction of motion of vehicle, the air resistance decreases.
