Friday, October 04, 2013

Exam time

Without understanding a word of Hebrew, calculate Q (flow in cu.m./hour) and P (pressure in Pascal) in point B  (the highest point of the pipe). To help you, I made a small breathing hole in the pipe exactly at Point B.

Star of Renpham said...

http://theaviationist.com/2013/10/03/france-strike-plans/#.Uk8u6hS5fUM

Javier said...

Pressure at point B will be atmospheric pressure ( thanks to your breathing hole), so no flow, Q=0

J said...

Javier: Great! You are among the upper half of my class. Many suspect that there is a catch and spend time in calculations. Did it took you much time to get the result?

spagetiMeatball said...

How would you solve if there was no hole, pascal's law?

J said...

Bernouilli

J said...

Then you may use Moody diagram. Or calculate Reynolds number. You can do it also by Poiselle.

spagetiMeatball said...

Hmm..googling makes it look much harder without the hole. You do your students much favor.

J said...

I do not. They get the pipe without the hole. Of course not exactly the same question nor the same values.

Javier said...

Well, it took me about half a minute, but I am an engineer...

And don´t be very hard on your students. Exams are stressful and may hinder correct reasoning.

But you can try this with them: No breathing hole, but make the height between the point B and surface of water bigger than 10 m...

Just don´t tell them it was my idea

J said...

I'll not tell them it was your idea. But I'll change the question to:

"Calculate the distance of the pipe from the water surface to Point B where the siphon stops operating. Explain why. The temperature is 25 Celsius."