# Homework Help: Bernoulli's principle

1. Dec 5, 2006

### fro

Liquid flows through a 4cm diameter at 1m/s. There is 2cm diameter restriction i n the line. Find fluid velocity in restriction.

$$p_1+ \rho\cdot g \cdot y_1 + \frac{1}{2}\rho \cdot(v_1)^2 = p_2+ \rho \cdot g\cdot y_2 + \frac{1}{2}\cdot \rho\cdot(v_2)^2$$

I know I have to use Bernoulli's principle to solve this. I am confused as to if I use the diameter or radius in the problem for the height. Can I cancel out p1 and p2?

Last edited: Dec 5, 2006
2. Dec 5, 2006

Unless I'm missing something, you could solve this by simply stating A1v1 = A2v2, where A1 and A2 are the areas of the cross sections of the pipe.

3. Dec 5, 2006

### fro

Thanks, I got it.

4. Dec 5, 2006

### fro

Here is a slightly different one:
Water flows at 12m/s with pressure of 3X10^4 N/m^2. If the pipe widens to twice its original radius, what is the pressure in the wider section?

I am trying to plug everything to Bernoulli's principle. Problem is that both the pressure and radius is unknown. Any hints as to how I should start this problem? Thanks.

5. Dec 5, 2006