Here's why:

* Newton's First Law of Motion: An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

* Constant Velocity: The car is traveling at a constant velocity of 20 meters per second westward. This means its speed and direction are not changing.

* No Acceleration: Since the velocity is constant, the car is not accelerating.

* Zero Net Force: Newton's Second Law of Motion states that force is equal to mass times acceleration (F = ma). If the acceleration is zero, the net force must also be zero.

In simpler terms: If the car is moving at a steady speed in a straight line, there's no need for any extra force to keep it going.