Question

a person is standing in an airplane that flies horizontally in a straight line at a steady speed of 500 mph. which of the following free - body diagrams for the person is the most realistic one under these conditions? (the meaning of the symbols is as follows: $vec{f}_{k}$ = kinetic friction, $vec{f}_{s}$ = static friction, $vec{n}$ = normal force, $vec{f}_{g}$ = gravity, $vec{f}_{thrust}$ = thrust force.
diagram a
diagram b
diagram c
diagram d
diagram e

Explanation:

The airplane moves at constant straight-line speed, so the person is in equilibrium (net force = 0). Vertically, gravity $\vec{F}_G$ pulls down, and normal force $\vec{n}$ pushes up, balancing each other. Horizontally, the person moves with the plane at constant speed, so there is no horizontal acceleration. This means no horizontal forces (thrust, friction) act on the person, as these would create an unbalanced force and acceleration.

Answer:

B. Diagram B