Final answer:
The magnitude of the upward-directed lift force exerted by the air on the airplane is approximately 1,176,000 N.
Step-by-step explanation:
To calculate the magnitude of the upward-directed lift force exerted by the air on the airplane, we need to consider the relationship between lift force and the speed of air over the wings. According to the given information, the airplane is in level flight at a speed of 900 km/h. To simplify the calculation, we need to convert the speed to m/s.
900 km/h = 900,000 m/h = 900,000/3600 m/s = 250 m/s.
Now, let's use the rule of thumb mentioned in the reference information: wings should produce about 1000 N of lift per square meter of wing.
Given that the airplane has a mass of 120,000 kg, we can calculate the magnitude of the lift force using the following formula:
Lift force = Mass of the airplane * Acceleration due to gravity
Lift force = 120,000 kg * 9.8 m/s^2 = 1,176,000 N
Therefore, the magnitude of the upward-directed lift force exerted by the air on the airplane is approximately 1,176,000 N.