Topic: Fluid Mechanics
If the stream function of two dimensional flow is psi = 5xy, then the velocity at a point (3, 4) is
- A. 25 m/s
- B. 20 m/s
- C. 7 m/s
- D. 5 m/s
Answer: A. 25 m/s
Explanation: Velocity in x-direction U = d(psi)/dy = 5x -> U(3,4) = 15 m/s. Velocity in y-direction V = -d(psi)/dx = -5y -> V(3,4) = -20 m/s. Resultant velocity V' = $\sqrt{U² + V²}$ = $\sqrt{15^2 + (-20}$^2) = 25 m/s.