Question

Vertical sections of a wing of a fan are shown in the following figures. The maximum upthrust will be in figure.
A.

B.

C.

D.

Answer 1

Hint: In the first figure, the fan shows thrust in the upward direction. That is, the air moves faster in an upward direction, because of low pressure. In the case of figure two the thrust is in downward direction. In the third figure, there is no thrust. Whereas for the last figure the upward and downward thrust cancels and the resultant thrust will be zero.

Complete answer:
In the first figure, the fan shows thrust in the upward direction. That is, the air moves faster in upward direction, the velocity is greater in upward direction thus here pressure is low. The pressure at the lower end is greater. Hence maximum upthrust will be in upward direction.
The second figure is just opposite to the first one, hence thrust is in downward direction. The air moves faster in downward direction, the velocity is downward direction thus here pressure is low. The pressure at the upper end is greater. Hence maximum upthrust will be in downward direction.
In the third figure the pressure at both the ends are the same. Hence, there is no thrust here.
The last figure is a combination of first and second one. Hence, the fan shows thrust in the upward direction as well as in the downward direction. Thus the resultant thrust cancels and the resultant thrust will be zero.

So, the correct answer is “Option A”.

Note:
Thus the thrust can be defined as force that exerts on liquid or gas. Upthrust depends on pressure at the top and bottom of the object. Thus in the first figure, the fan shows thrust in the upward direction. That is, the air moves faster in an upward direction, because of low pressure. In the case of figure two the thrust is in downward direction. In the third figure, there is no thrust. Whereas for the last figure the upward and downward thrust cancels and the resultant thrust will be zero.