Final answer:
The statement "Supersonic airflow takes a 5 expansion turn" is true.
Step-by-step explanation:
When considering an image showing a velocity vs. time graph for a jet car, the slope at any point on the graph indeed represents the car's acceleration. If the slope is constant and equals 5.0 m/s² at all points, then the car's acceleration is indeed 5.0 m/s² at every point in time.
Regarding the statement about a comet reaching its greatest speed as it travels near the sun, it is true that comets tend to achieve higher speeds as they approach the sun due to the sun's gravitational pull. However, relativistic effects on a comet's tail are not typically significant. The lengthening of the comet's tail is primarily due to solar radiation pressure and the solar wind interacting with the material in the comet's tail, rather than relativistic effects.
Lastly, when discussing the performance of a propulsion mechanism, it's too generous to assume performance without considering specific details. For example, propellers are effective at certain speeds and altitudes but aren't typically used for supersonic airflows as the question suggests.