1 there must be no forces applied to the car.
The 3rd answer is the correct one. Since the velocity is constant, there is no change in velocity, thus zero acceleration. To actually say that there are no forces acted on the car is wrong assumption. the force direction to the left (thrust) is there but it has been eliminated by the force acted to the right (friction). Thus, the net force equal to zero. Based on F=Ma, there will be no acceleration, in other word, no change in velocity, constant velocity.
Source(s): High School subject
Constant velocity means the forces acting are in equilibrium (net force is zero)
If they were not, Newton’s second law (F = ma) would apply and the car would accelerate changing the velocity.
so 3 is correct.