# Homework Help: Scuba diving pressure physics question

1. Sep 18, 2008

### girlinterrupt

Hi Everyone,

I was wondering if someone can look over my answers and see if I have answered them correctly.

1. The problem statement, all variables and given/known data

Janet decides to go scuba diving. Her scuba diving apparatus is set up so that the pressure in the bottle is regulated so she can breathe the air at a pressure which matches the pressure of the surrounds (air or water pressure). The bottle has a pressure gauge that shows the gauge pressure in the bottle and she has a backup pressure gauge on her wrist that shows the absolute pressure of the surrounds. She starts by pressurising her gas bottle to twenty times atmospheric pressure.

a) What is the absolute pressure in her gas tank?

b) What does the pressure gauge on the gas tank read?

She dives quickly down to a shipwreck that she is exploring. When she is at the wreck she notices that her wrist gauge shows 5.05 ×10^5Pa. Having achieved high grades in her physics subject, she realises that she can calculate her depth from the gauge pressure.

c) If we assume the water has a density of 1000kgm-3, to what depth has she dived?

2. Relevant equations

Pabs = Pguage + Patmosphere
standard atmospheric pressure = 101kPa = 101000 Pa

Pressure = Density x Height x Gravity

3. The attempt at a solution

a)

Using:
standard atmospheric pressure = 101kPa = 101000 Pa
and
inside the tank is initiallt set to: 20 x 101000 = 2020000 Pa

Pabs = Pguage + Patmosphere
Pabs = 2020000 + 101000 = 2121000 Pa = 2.121x10^6 Pa

b)

Pressure guage on the tank is relative, so it would state that it is 20...?

c)

Wrist guage measurement is the absolute pressure, which = 5.05 ×10^5Pa
Water density = 1000kgm-3
Gravity = 9.8m/s^2

Using:
Pressure = Density x Depth x Gravity

So...
Depth = Pressure / Density x Gravity
Depth = 5.05 ×10^5 / 1000 x 9.8 = 51.53m

Thanks, I appreciate the how helpful everyone has been hear! :)

- girlInterrupt

Last edited: Sep 18, 2008