# Gauge pressure at the bottom?

## Homework Statement

A test tube standing vertically in a test tube rack contains 3.8 cm of oil, whose density is 0.81 g/cm3 and 6.4 cm of water. What is the gauge pressure on the bottom of the tube? The acceleration of gravity is 9.8 m/s2. Answer in units of Pa

## Homework Equations

P1-Po=$$\rho$$oilgh1+$$\rho$$H2Ogh2

## The Attempt at a Solution

P1-Po= (810 kg/m3)(9.80 kg m /s2)(0.038 m) + (1000 kg/m3)(9.80 kg m/s2)(0.064 m)

P1-Po= 929 Pa

Is the work and answer right? TIA

They are indeed correct.

Thank you! Actually, I wonder whether you should also consider atmospheric pressure.

Also, why is it P1-P0 and not +?

^It came out right with 929 Pa.
The way the prof had shown it in class is P1-P0:

P2=Po+$$\rho$$oilgh1

P1=P2+$$\rho$$H2Ogh2

P1=Po+$$\rho$$gh1+$$\rho$$gh2

P1-Po=$$\rho$$gh1+$$\rho$$gh2

Oh ok, it was down to notation, then.
When I thought you might need the atmospheric pressure is because I was calculating P1, but you needed P1-P0. :)