It's due to Inertia. The law of Inertia states that a body will try to retain its movement state if possible. This means, if a body is at rest, it will try to remain at rest using forces. Similarly, if it's in movement, it will try to remain in movement.
In this example, the plane is moving forwards, and so do the seats, which in turn push the passenger forwards.The force felt is Inertia acting on the body, trying to counter the movement.
The formula we will be using is;F = G m1 m2 / r^2
F earth = 308N
F moon = G me m2 / (81.3 * 0.27^2 RE^2) = 1/5.927 G me m2 / RE^2 = F earth / 5.927 = 52 N is the force of the earth
So the answer in this question is 52 N.
<span>When an object travels in a curved path, there must be a force acting toward the center of the circular trajectory. This force is called "centripetal force", and it cause an acceleration of the object, called "centripetal acceleration". The effect of this acceleration is that the velocity of the object changes in direction: however if the circular motion is uniform, the speed (=the magnitude of the velocity) does not change. In this case, the magnitude of the centripetal force is given by
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where m is the mass of the object, v its velocity, and r the radius of the circular path.</span>
My educated guess : 21.2 deg