Skier pushes him self along the snow on flat ground he feels Erizo cents on his body which way

Forward

Explanation:

Since the skier pushes himself along the snow on flat ground and he feels air resistance, he will only feels air resistance when he starts moving (unless wind is blowing in opposite direction). The net force vector is dependent on the amount of force applied by the skier here we assume that skier continues to move in forward direction. The net force vector will act in the direction of acceleration, since the skier continues to move in the forward direction, therefore the net force vector will also point in the forward direction.

c)as speed changes, wavelength and frequency change.

everything changes!

d) physical means can be used to separate the components of air.