Answer
Both of the statements can be explained by Newton's first law.
Work Step by Step
Both of the statements can be explained by Newton's first law.
In case (A), when your car suddenly comes to a halt by an external force, this force, however, does not affect you. Your body, according to Newton's first law, continues moving forward at a constant velocity, resulting in you lunging forward. You can only stop when there is an external force opposing this motion, which might come from the steering wheel for example.
Similarly, in case (B), before the car's acceleration, both your car and you are static. The engine forces the car, but not you, to rapidly acceleration. As a result, you continue to be in a state of rest while your car and the seat in the car are already moving forward. That is why you are pressed backward against the seat.
