If a fly is flying from the back of the plane towards the front while the plane is traveling at a constant speed, the speed of the fly relative to the ground (outside the plane) will depend on two factors: the speed of the airplane (x speed) and the speed at which the fly is flying within the plane.
If the fly is flying in the same direction as the plane: In this case, the speed of the fly relative to the ground will be the difference between the fly's flying speed (relative to the plane) and the speed of the airplane. So, the speed of the fly relative to the ground will be x speed (airplane speed) + fly's speed.
If the fly is flying in the opposite direction as the plane: In this case, the speed of the fly relative to the ground will be the sum of the fly's flying speed (relative to the plane) and the speed of the airplane. So, the speed of the fly relative to the ground will be x speed (airplane speed) - fly's speed.
In either case, the fly's speed relative to the ground will be either faster or slower than the airplane's speed, depending on the direction in which the fly is flying within the plane.
To clarify further, let's consider an example:
Suppose the airplane is flying at a constant speed of 500 km/h, and the fly is flying within the plane at a speed of 5 km/h towards the front of the plane.
If the fly is flying in the same direction as the plane, its speed relative to the ground will be:
500 km/h (airplane speed) + 5 km/h (fly's speed) = 505 km/h
So, the fly will be traveling at 505 km/h relative to the ground.
If the fly is flying in the opposite direction as the plane, its speed relative to the ground will be:
500 km/h (airplane speed) - 5 km/h (fly's speed) = 495 km/h
So, the fly will be traveling at 495 km/h relative to the ground.
In both cases, the fly's speed relative to the ground is different from the airplane's speed, either faster or slower depending on the direction of the fly's flight within the plane.