A 7.0kg skydiver is descending with a constant velocity

Air resistance: 68.6 N

Explanation:

For the skydiver falling down, there are two forces acting on him:

- The force of gravity, of magnitude

where

m = 7.0 kg is the mass of the skydiver

is the acceleration of gravity

This force acts in the downward direction

- The air resistance, R, in the upward direction

So the net force on the skydiver is:

According to Newton's second law of motion, the net force is also equal to mass times acceleration:

However, in this problem the skydiver is falling at constant velocity, so his acceleration is zero:

Therefore, the net force is zero:

And so we can find the magnitude of the air resistance, which is equal to the weigth of the skydiver: