Calculate pressure using Bernoulli's equation

[09matthew]

Homework Statement

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!

Homework Equations

The Attempt at a Solution

 

[drvrm]

You have been given a milkshake (ρ = 1200kg/m^3). The glass is 200mm tall a straw 8mm diameter and 300mm long.[/QUOTE
i think one should calculate the pressure difference required for the liquid to rise to the upper point of the straw and the velocity of the liquid may be sufficient only to pour out in the mouth- one can take a unit volume for estimation of the required pull from the lungs.

 

[drvrm]

Show that human lungs would be unable to drink the milkshake through a vertical straw.

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!

 

[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)?

 

[drvrm]

and also, is z1 = 200mm (size of the cup) and z2 = 300mm (size of the straw)?

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.