Question

The below figure shows a pipe with a circular cross section of diameter 5 cm on the left end and a square cross section with diagonal 5 cm on the right end. Water enters the left end with a velocity 20 m/s and leaves the right end with a velocity V2. Find V2 (neglect losses in the pipe).

(a) V2 cannot be found as the length of the pipe is not given

(b) V2 cannot be found as the intermediate cross sections are not given.

(c) 31.41 m/s

(d) 20 m/s

I got this question in a job interview.

My doubt stems from Introduction to Fluid Dynamics topic in section Fluid Dynamics of Fluid Mechanics

Answer 1

Right choice is (c) 31.41 m/s

The best explanation: Apply continuity equation A1V1 = A2V2. We find that the velocity comes out to be 31.41 m/s. The question can be answered without calculations if the concept is known. V2 neither depends upon the length of the pipe nor on the intermediate cross sections if losses are neglected.