KVPY 2020-21 SA Exam Previous Papers

Question : 21 of 80

Marks: +1, -0

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

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

As the platelets enter a constriction, the platelets get squeezed closer together in the narrow region and hence the fluid pressure must rise there
As the platelets enter a constriction, pressure is lower there
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
Pressure is same in all the parts of the artery

Solution:

Using equation of continuity

A_1V_1 = A_2V_2

Thus as area reduces speed would increase.

V_II > V_I

Now as per Bernoulli’s theorem

{1}/{2} \ρV_{1}^{2}+P_{1}={1}/{2} \ρV_{{I}}^{2}+P_{{II}}

R={1}/{2} \ρ(V_{11}^{2}-V_{1}^{2})+P_{I}

⇒P_{1}>P_{{II}}

. Thus pressure at constriction is less.

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