Forces and Speed

1. Apr 8, 2007

dvyu

It takes 30.0s to fill a 2.00-L container with water from a hose with a constant radius 1.00cm. The hose is held horizontally. Determine the speed of the water being ejected from the hose.

I have attempted this question, but I have got a different answer to my textbook. I may however be going about this the wrong way.

Attempt:
4p(0.01)/30^2 = 2pV/30
V = 2.09E-3 m/s

2. Apr 8, 2007

What exactly does your attempt represent?

How is the flow defined and how can you calculate it from the given data? Further on, how does the flow relate to the area and speed?

3. Apr 8, 2007

dvyu

oh yes - I was using acceleration formulae
So, I should be using
area = flow/velocity and flow = Litre/second

4. Apr 8, 2007

Try to do so.

5. Apr 8, 2007

dvyu

I have used that formula -
velocity = (2/30)/(3.14*0.01^2) = 212.2m/s
The thing is, my text book gives the answer as 21.2cm/s, and my answer converts to 2.12cm/s. Am I wrong or is the text book wrong?

6. Apr 8, 2007

7. Apr 8, 2007

dvyu

Okay - can you tell me where I went wrong, because I can't see where I went wrong

8. Apr 8, 2007

You went wrong with the flow units. 1 [L] = 1 [dm^3]. Convert to [cm^3].

9. Apr 8, 2007

dvyu

okay, thanks, I'll try again

~it's worked out, thanks for your help

Last edited: Apr 8, 2007
10. Mar 10, 2011

2much

Sorry, a better question is why is area equal to flow / velocity and since 1 L equals 1dm wouldn't 1L equal to 10cm? So than why do we have r as 0.1?
velocity = (2/30)/(3.14*0.01^2) = 212.2m/s

Oh i see you are converting 1cm into dm. I still can't grasp how area = flow / velocity?

Last edited: Mar 10, 2011