Question

an airplane is traveling in level flight at a constant velocity. l is the lift, w is the weight, t is the thrust, and d is the drag. which of the diagrams is the correct free - body diagram for the airplane? multiple choice options: figure 2, figure 4, figure 3, figure 1, figure 5

Explanation:

For an airplane in level, constant - velocity flight, the net force is zero (Newton's first law). In the vertical direction, lift ($L$) must balance weight ($W$) ($L = W$). In the horizontal direction, thrust ($T$) must balance drag ($D$) ($T = D$). We need to find the free - body diagram where vertical forces ($L$ and $W$) are equal and opposite, and horizontal forces ($T$ and $D$) are equal and opposite.

Answer:

To determine the correct answer, we analyze the force balance:

1. Vertical Forces: Lift ($L$) acts upward, weight ($W$) acts downward. For level flight, $L = W$ (magnitudes equal, directions opposite).
2. Horizontal Forces: Thrust ($T$) acts in the direction of motion, drag ($D$) acts opposite to motion. For constant velocity, $T = D$ (magnitudes equal, directions opposite).

We assume that Figure 3 (from the given options) has $L$ opposite to $W$ (vertical balance) and $T$ opposite to $D$ (horizontal balance). So the correct option is the one corresponding to Figure 3 (the option with Figure 3 selected). If we assume the options are labeled as per the figures (e.g., if Figure 3 is one of the radio - button options), the answer is the option for Figure 3.

(Note: Since the exact figure details are a bit unclear from the text - based description, but the key is the force balance. In a typical correct free - body diagram for level, constant - velocity flight, vertical forces $L$ and $W$ are equal and opposite, horizontal forces $T$ and $D$ are equal and opposite. So the figure with $L$ upward, $W$ downward, $T$ forward, $D$ backward, with equal magnitudes for each pair is correct.)