# Homework Help: Venturi meter help

1. Aug 12, 2008

### ahello888a

Venturi meter help!!!

1. The problem statement, all variables and given/known data
A venturi meter is measuring the flow of water; it has a main diameter of 3.0 cm tapering down to a throat diameter of 1.0 cm. If the pressure difference is measured to be 16 mmHg, what is the speed of the water entering the venturi throat?

2. Relevant equations

Got that equation from a previous part of the problem where it asked me to "Show that the flow speed measured by a venturi meter (see Figure 13–32 in the textbook) is given by the relation"

3. The attempt at a solution

I used $$\rho$$ to be density of water. I converted the diameters to radius in meters. I converted the pressure to "m-Hg". I get 1.77*10^-5. The homework program keeps telling me I'm wrong. I can't see what I'm doing wrong. Thank You for the help!

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2. Aug 13, 2008

### tiny-tim

Hi ahello888a!

(you said mmHg as the top, and m Hg at the bottom … is that a typo?)

erm … we need to see your full calculation if we're going to find out where it's wrong!

3. Aug 13, 2008

### stewartcs

Re: Venturi meter help!!!

Start by writing out the energy balance using the Bernoulli equation.

Hints:
Assume the elevation change is zero.
Neglect the small friction.
Use the continuity equation.

Hope this helps.

CS