Q41 / 55 · KVPY 2020 (SA) · Physics

The platelets are drifting with the blood flowing in a streamline flow through a horizontal artery as shown below:

Figure

Artery is contracted in region II. Choose the correct statement.

  • A
    As the platelets enter a constriction, the platelets gets squeezed closer together in the narrow region and hence the fluid pressure must rise there.
  • Correct answer
    B
    As the platelets enter a constriction, pressure is lower there.
  • C
    The artery's cross section area is smaller in the constriction and thus the pressure must be larger there because pressure equals the force divided by area
  • D
    Pressure is same in all the parts of the artery

Solution

Figure

Using equation of continuity

A1V1=A2V2

where A1 & A2 are cross-section area of region I & region-II.

as A2<A1

⇒V2>V1

Using Bernouilli's equation

P+12ρV2= constant

as V2>V1

P2<P1

therefore pressure will be lower at constriction.

Hence, the correct answer is option: 'B'.

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