# Homework Help: Pressure with fluids

1. Jan 14, 2009

### dimpledur

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

A submarine is at a depth of 500 m under the water. The force on a circular hatch of 1.00 m in diameter due to the seawater (density = 1,025 kg/m3) pressure from outside the submarine is:

2. Relevant equations

F=PA
P2-P1=pgd

3. The attempt at a solution

F=(pgd+P1)A

where A = pi*r^2

When I plug in all the values, I cannot get the answer.

2. Jan 14, 2009

### dimpledur

F=[(1025kg/m^3*9.8N/kg*500m)+1.013x10^5 Pa][pi*(0.5m)^2]
F=4.02x10^6 N

I have no clue where I am going wrong, in fact I thought this was an easy concept?

3. Jan 14, 2009

### dimpledur

Did I mess up somewhere with the units?
Was I wrong to assume the pressure at the submarine would be P=pgd + 1.013x10&5 Pa?
I don't know....

4. Jan 14, 2009

### Stovebolt

What is the answer supposed to be?

The only thing I can see would be that the question is asking for the force due to the pressure from the seawater, which might mean the water only, not the total pressure (which would include atmospheric pressure, as you did above).

5. Jan 14, 2009

### dimpledur

That answer is not there either, though.

a. 2.45 × 106 N.
b. 3.95 × 106 N.
c. 4.94 × 106 N.
d. 5.50 × 106 N.
e. 6.34 × 106 N.

6. Jan 14, 2009

### dimpledur

Nevermind figured it out thanks!