What Determines the Flow Speed in Differently Sized Horizontal Tubes?

[Hypnos_16]

Homework Statement

Seawater flows through a horizontal tube of diameter 3.00 cm that is joined to a second horizontal tube of diameter 1.70 cm. The pressure difference between the tubes is 7.25 kPa. What is the speed of flow in the first tube?

Homework Equations

I thought it was P1 + 1/2 pv²
turns out it isn't

The Attempt at a Solution

i don't know if it's cause I'm stressed, or just missing something, i cannot get this question to work.

 

[edgepflow]

Note: P1 + 1/2 p v1^2 = constant = P2 + 1/2 pv2^2.

Do you also need to apply the conservation of mass ?

 

[Hypnos_16]

The conservation of mass? and what "Constant" are you talking about there?

 

[edgepflow]

The conservation of mass will allow you to relate the speed of the fluid in the two different size pipes and the pipe diameter.

Bernoulli's equation says P + p v^2 / 2 + p g h = constant. So if you know these values at one point, you know them at the other.