# Homework Help: What will be the velocity of flow ?

1. Dec 16, 2012

### BrnoStudent

Water flows through a rigid tube, the radius of which is 1 cm. What will be the velocity
of flow in a part of the tube with a radius of 3 cm?

Please show your working and any equations that you use, no matter how basic you think it is. If there is no working to show then just explain how you arrived at your answer. I know the answer is e, I just don't know why. Thank you.
a) 3 m.s-1
b) one third of the original value
c) one sixth of the original value
d) three-times bigger than the original value
e) six-times bigger than the original value

2. Dec 16, 2012

### sophiecentaur

This is another question that should be posted in the Homework and Coursework Questions thread. If you want an answer then you need to show you have attempted to answer by posting your own ideas.

3. Dec 16, 2012

### BrnoStudent

If I knew what to do, I would not be asking for help in the first place. This is a biophysics question from med school and it's an exam question, not a homework question. I'm practicing for my exams.

4. Dec 16, 2012

### sophiecentaur

It's up to you. Have you looked at any information about the topic or did you come straight here?
I googled 'liquid flow velocity' and that threw up 'Volumetric Flow rate' - which gave me what you want. If you want to be a medic, then that should be the sort of thing you'd expect to do - ain't it?
Just giving you the answer would not do anything for your ability to answer a similar question, would it? You say you want to pass an exam.

5. Dec 16, 2012

### BrnoStudent

I don't "want" to be a medic, I already am. I've been scanning through a 400page biophysics text book, I also have 4 other exams this week, if there's anything that I can do to make my life easier at this point I will. Once again, thank you for your reply. I will ask the question in another section.

6. Dec 16, 2012

### sophiecentaur

I could suggest a bit more tactful way of wording your original post, then. i.e. "Do us a favour chaps, I have this looming exam . . . ."?

7. Dec 16, 2012

### K^2

The way question is stated, the correct answer is 1/9th. I can think of several different ways to mis-interpret the question, giving me results up to factor of 81, but answer e) isn't even on the radar. Where'd you get this from?

8. Dec 16, 2012

### BrnoStudent

They are practice exam questions from my uni and it says the answer is e on the paper.

9. Dec 16, 2012

### cjl

Well, it's wrong. I agree with K2 - the correct answer is 1/9.

10. Dec 16, 2012

### sophiecentaur

If the OP googles Volumetric Flow, the main hits give the formula and the reasoning behind it. The 'letter' given in the answer to multichoice questions is useless for learning. The theory is what counts.

11. Dec 16, 2012

### cjl

True. In this case, I would argue that the letter is actually worse than useless - it is detrimental (since it indicates an incorrect answer, unless there is some background or additional information with the problem that we have not been given).

12. Dec 16, 2012

### Staff: Mentor

This thread has been moved from the General Physics forum where it was originally mis-posted. Because some help had already given, I chose to move it and not delete it, which explains why the first post does not follow the template.