What is the acceleration of the car during this 4.0-second interval?

The answer to this is 2.5 m/s2 west. Velocity and acceleration are known to work well together. When there is a change in the velocity of an object, this is already an obvious sign that the object is accelerating or moving towards one direction.

Velocity is a bit complicated to understand for some people probably because it would also rely on direction and magnitude. Some feel that acceleration and velocity are the same but this is not true.

They are closely related to each other though so it is not surprising that some people find this a bit confusing. Remember that velocity and acceleration usually point in the same direction when the object speeds up.