# Calculate pressure using Bernoulli's equation

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1. Mar 9, 2016

### 09matthew

1. The problem statement, all variables and given/known data
You have been given a milkshake (ρ = 1200kg/m^3). The glass is 200mm tall a straw 8mm diameter and 300mm long. Show that human lungs would be unable to drink the milkshake through a vertical straw. (answer should be around 3000Pa)

I have no idea what to do as I don't know how to find the speed and also not sure if P1 is atmospheric pressure or not. Any help would be greatly appreciated!

Thank you!
2. Relevant equations

3. The attempt at a solution

2. Mar 9, 2016

3. Mar 9, 2016

### drvrm

suppose a person sucks out air from the straw the liquid can rush to the top by difference of pressure - the atmospheric pressure and the air pressure in side the mouth which is air pressure in the lungs- try to calculate it and see how it comes out!

4. Mar 9, 2016

### 09matthew

Sorry, I'm still not so sure where to start... how would i get the pressure difference? and also, is z1 = 200mm (size of the cup) and z2 = 300mm (size of the straw)?

5. Mar 9, 2016

### drvrm

one can dip the straw ,so that the height difference is only( z2 -z1) -the human lung can take average about 6 litres of air.