Bernoulli's Principle Question

I have this problem:
Water flowing in a horizontal pipe is at a pressure of 1.5 105 Pa at a point where its cross-sectional area is 1.50 m2. When the pipe narrows to 0.400 m2, the pressure drops to 1.16 105 Pa.
(a) Find the water's speed in the wider pipe
(b) Find the water's speed in the narrower pipe.

I tried using Bernoulli's Principle but I can't get it.
I took the (p)(g)(h) out of both sides since the pipe's height doesn't change. And then I tried solving for v1 and v2 but there are two unknowns and I don't know what to do after that....

If anyone could help, that would be awesome.
Thanks in advance.


Science Advisor
Homework Helper
HINT: The flow is horizontal so gravity is not a consideration. You have Bernoulli's Principle to work with (pressure + kinetic energy per unit volume = constant) but you also have a continuity condition (flux times cross section = constant).
Hi, thanks for the info.

I tried using the equation, P + 1/2pv^2 = P + 1/2pv^2
and I ended up with two unknowns, the two different v^2.
So then I tried solving for 1 v using the AV=AV equation and then plugging it back into the first equation but that didn't come out right either...

Anymore suggestions?
Could anyone show me where I am messing this up?

Doc Al

You're approach seems correct. Show the details of your calculation.

The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving