Look at the speedometer.
Whatever the posted speed limit is.
In full speed and chek the speed
This question makes no sense, what do you mean? the speed of the car does not dictate the posted speed limit.
90
It sets the speed at which Highway Safety Engineers determine can be driven safely on that stretch of roadway.
Its speed is 55 mph, and if the highway doesn't curve, then its acceleration is zero.
Well you see considering that highway workers work on the highway and if the speed limit was raised, then there's more of a possibility of a car "flying" down the highway and hitting the highway worker
Speedometer can determine a car's normal and maximum speed.
If its speed is constant, its acceleration is nil.
Generally, the average car speed is whatever the speed limit is. While some go over and under, others stay right on the speed limit, making it the average.
A beam of electromagnetic waves is bounced off the car
Distance that can be traversed at that speed in that amount of time.