Calculating Velocity of Water in a Circular Pipe

[kitty9035]

Homework Statement

Water is flowing at 1 m/s in a circular pipe. If the diameter of the pipe decreases to four-ninth its former value, what is the velocity fo the water downstream?

Homework Equations

AV=AV

3. The Attempt at a Solution [/b
(Area1)(Velocity1)=(Area2)(Velocity2)
then...
(A1)(1 m/s)=(4/9)A1(V2) ?
or
A1=(4/9)(V2)

Is that right what would u do next??

 

[durt]

Rewrite the area in terms of its diameter, and then try again.

 

[AngeloG]

Indeed, remember the area for a circle? *circular* being the key word =).

 

[snowJT]

couldn't you just with what your given calculate the volumetric flow rate then, then apply Q = AV to get the velocity in the second pipe.. that's how I would do it

 

[AngeloG]

A1V1 = A2V2, since the density is uniform/incompressible.

You could do as you say, but then you'd have the equation:
A1 * (delta L1) / delta t = A2 * (delta L2) / delta t

A1V1 = A2V2 is a better one to use; well more "simple" one.