Calculate Water Speed in Venturi Meter

[ahello888a]

Venturi meter help!

Homework Statement

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?

Homework 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"

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!

 

[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!

 

[stewartcs]

Homework Statement

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?

Homework 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"

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!

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