Fig. Represent vertical sections of four wings moving horizontally in air. In which case the force is upwards
A.
B.
C.
D.

Hint: The force acting normal to the surface is the product of the pressure and the area of the surface. The net force acts in the direction of the force with larger magnitude if two forces are acting in opposite directions.

Complete step by step solution:
The force on the wing will act vertically upward if the force acting upward is greater than the force acting downward. As the thickness of the wing is insignificant to consider the pressure variation due to atmospheric air with height, so the pressure acting above the wing is assumed to be equal to the pressure below the wing.

For the first shape of wing,

The effective area of the upper portion of the wing is less than the area below the wing. So, the force acting on the upper portion in the downward direction is less than the force acting on the lower portion in upward direction. Hence, the net force acting on the wing is in upward direction.

For the second shape of wing,

The effective area of the lower portion of the wing is less than the area of the upper portion of the wing. So, the force acting on the upper portion in the downward direction is greater than the force acting on the lower portion in upward direction. Hence, the net force acting on the wing is in downward direction.

For the third shape of wing,

The effective area of the lower portion of the wing is equal to the area of the upper portion of the wing. So, the force acting on the upper portion in downward direction is equal to the force acting on the lower portion in upward direction. Hence, the net force acting on the wing is zero.

For the fourth shape of wing,

The effective area of the lower portion of the wing is equal to the area of the upper portion of the wing. So, the force acting on the upper portion in downward direction is equal to the force acting on the lower portion in upward direction. Hence, the net force acting on the wing is zero.

Therefore, the correct option is A.

Note: The net upward force on the wing is so that it balances the weight of the aircraft so that it moves horizontally. Moreover, wings are airfoils that provide lift when they are moved quickly through the air. They come in a variety of sizes and forms. Different wing designs might offer specific desirable flying characteristics.