The stream function is given by the expression ψ = 2x2 - y2.  What is the resultant velocity at a point denoted by x = 2 and y = 3 ?

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UPSC ESE Prelims (Civil) 20 Feb 2022 Official
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  1. 10
  2. 12
  3. 15
  4. 18

Answer (Detailed Solution Below)

Option 1 : 10
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Detailed Solution

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Explanation:

Given;

Stream function 

ψ = 2x2 - y2

As per Cauchy Riemann equations

\(u = -\frac{\partial\psi}{\partial y}\) = - (-2y) = 2y

\(v = \frac{\partial\psi}{\partial x}= 4x\)

At (2,3),

u = 6 unit

v = 8 units

The resultant velocity is

(V) \(=\sqrt{u^2+v^2}\)

\(=\sqrt{6^2+8^2}\)

V = 10 units

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