Question

An application of Bernoulli's equation for fluid flow is found in ________ .
A. viscosity meter
B. capillary rise
C. Hydraulic press
D. dynamic lift of an aeroplane

Answer 1

By the virtue of Bernoulli's principle, for an incompressible, non-viscous fluid, the sum of pressure energy, gravitational potential energy and kinetic energy (due to fluid velocity) per unit volume remains constant along a flow which is streamlined.

Complete step by step answer:
Major applications of Bernoulli's theorem include venturimeter, atomizer (or sprays), spinning of a ball, etc. Consider the case of a spray. When we press a spray bottle, the pressure inside it decreases as the air already rushed out as we pressed the bottle. To balance the decreased pressure energy, the level of the liquid rises in the can and it comes out along with the air in an attempt to balance the gravitational energy part.
In case of a ball spinning through the air, its path gets curved due to Bernoulli's principle. As it moves forward, air rushes behind it. From one side, it opposes the spin and on another end, air moves along the spin. Due to this, the pressure on both sides becomes different and the velocity of the ball increases in the direction where pressure is less.
Similar to this example is the example of Dynamic lift of an aeroplane. The upper surface of the wing of an aeroplane is more curved as compared to the lower surface. As the plane moves, the air over the wing moves at a higher speed as compared to the air below the wing. Then according to Bernoulli's principle, the pressure above the upper surface decreases and the pressure below the lower surface increases. This pressure difference helps in lifting of an aeroplane.
Therefore the correct answer is option (D).

Note:
Bernoulli's theorem applies in the case when the fluid is non viscous so we can rule out option (A). Capillary rise occurs due to interplay of cohesive and adhesive forces of a fluid with the substance of Capillary (glass). Hydraulic press is an example of Pascal's law. All the options might be a little confusing so it is better to remember the basic definition of Bernoulli's principle in such cases.