Final answer:
A speedometer reading of 40km/hr shows the instantaneous speed, not the velocity, which also accounts for direction. A car can have a constant speed but still be changing its velocity if it's changing direction.
Step-by-step explanation:
If the speedometer of your Prom Limo has a speed of 40km/hr, it does not necessarily mean that the car has a constant velocity. While a speedometer shows the instantaneous speed of a vehicle, which is the rate of motion at a particular instant in time, velocity is a vector quantity that includes both speed and direction of motion. Therefore, even if the speed is constant, if there's any change in direction, then the velocity is not constant.
For example, while driving in a circular track at a constant speed, your speedometer would read the same speed throughout the journey, but your velocity would be changing at every point because the direction is continually changing. Therefore, a speedometer alone cannot confirm a constant velocity.