A car starts 10 m north of a reference point. It moves at a constant velocity over the next 5 s, reaching a position of 10 m south of the reference point. What is the car's average velocity?

  v = -4 m / s

Explanation:

The average speed of a body is defined by the distance traveled in a given time interval

     v = (x₂ -x₁) / (t₂ -t₁)

in this case the end point is x₂ = -10 m and the start point is x₁ = 10 m, the negative sign is because the point is below the reference that can be considered as zero point

let's calculate

     v = (-10 - 10) / 5

     v = -20 / 5

      v = -4 m / s

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.

because if the tool that you are using is not balanced it there would be false mass.