Question

If ψ=2x+3y represents stream function then what is the magnitude of velocity?

(a) 3

(b) 5

(c) 6.3

(d) 3.6

The question was posed to me in homework.

Question is taken from Single Variable Problems in portion Single Variable Problems of Finite Element Method

Answer 1

Right option is (d) 3.6

To elaborate: The magnitude of velocity (v) is   (V^2+U^2)^(1/2).

V=\(\frac{\partial  \psi}{\partial  y}\)=3 and U=\(\frac{-\partial   \psi}{\partial  x}\)=-2

v=(3^2+2^2)^(1/2)

v=(9+4)^(1/2)

=3.6.