# Homework Help: Pressure in a Lake

1. Oct 27, 2009

### Manda_24

1. The problem statement, all variables and given/known data
At the surface of a freshwater lake the air pressure is 1 atm. At what depth under water in the lake is the water pressure 4.5 atm?

2. Relevant equations
P=a+hgp
h=(P-a)/(g*p)

3. The attempt at a solution
h=(4.5x105 - 1x105)/(9.8*1000)=35.71
I also did the equation with 9,000 Pa converted to atm, which I think it what I'm supposed to do but I still get the incorrect answer.

2. Oct 27, 2009

### Gear300

Convert everything to pascals before using the equations. Also, be sure that the density you have for freshwater is in kg/m3. I'm not seeing anything wrong in your method, so I'm assuming the problem is in the units.

3. Oct 27, 2009

### JDHalfrack

"h=(4.5x105 - 1x105)/(9.8*1000)=35.71" Appears to be correct. If I am not mistaken, 10 m of water is roughly = to 1 atm. But, I am not 100% sure off the top of my head. If that's the case, it would make sense that 35 m of water would be about 3.5 atm plus the 1 atm from the atmosphere = 4.5 atm.

If you know, what is the answer supposed to be?

4. Oct 27, 2009

### Manda_24

Thanks, I just needed to convert the top to pascals, I thought I only had to do it to the bottom.