Final answer:
Without more data on the airplane's trajectory or descent rate, an exact second time when it reaches the height of 5000 meters cannot be determined. Theoretically and in perfect conditions, it could occur at twice the initial climb time to reach that altitude, minus the initial 4.5 minutes.
Step-by-step explanation:
The question pertains to the time it takes an airplane to reach a certain height twice during its ascent. First, we know that the airplane reaches a height of 5000 meters after approximately 4.5 minutes. This timing likely corresponds with the airplane on a climbing trajectory. The second time it reaches the height of 5000 meters would logically be on its descent after it has reached its maximum altitude and is coming back down. Without actual descent rates or total flight time data, calculating the exact second time it hits 5000 meters is not possible. However, as a typical approach to such problems, if we assume a symmetric flight path in the absence of air resistance and other practical considerations, the time taken to descend back to 5000 meters would be the same as the time it took to initially climb to that height. Thus, the other theoretical time when the airplane would reach 5000 meters is at twice the initial time, minus the original 4.5 minutes.