# Pressure in the Ocean

mantillab

## Homework Statement

I'm trying to understand the concept of pressure in fluids.

The pressure at 10m below the surface of the ocean is about 2.00×10^5 Pa.
Now consider he pressure at 20m below the surface of the ocean.
This pressure is:
a) twice that at a depth of 10m.
b) the same as that at a depth of 10m.
c) equal to that at a depth of 10m
plus the weight of a column of seawater 1m^2 in cross section and 10m high.
d) equal to the weight of a column of seawater 1m^2 in cross section and 20m high.

p=p_0 +pgh

## The Attempt at a Solution

Since pressure increases with depth, the pressure at 20m won't be the same as that at 10m. The pressure at a point 20m under the water is equal to the weight of the water above it and the pressure at the surface.

I don't think that (a) is the answer, because that would not take into account the pressure at the surface which isn't doubled. Answer choice (b) isn't correct because the pressure changes as the depth/height increases.

Answer choice (c) seems like it may be correct because it takes into account the pressure at the surface (p_0) and adds the extra weight of the increased depth, but would this conform to the equation: p=p_0 +pgh?

Answer choice (d) also seems like a possibility, except that it doesn't take into account the pressure at the surface at all and only refers to the weight of the sea water.

Any thoughts?

## Answers and Replies

Raze2dust
[
Answer choice (c) seems like it may be correct because it takes into account the pressure at the surface (p_0) and adds the extra weight of the increased depth, but would this conform to the equation: p=p_0 +pgh?

I don't get it...why won't it conform?

mantillab
I guess I was confused by the way the problem was worded. But now that I think about it, it makes perfect sense: the pressure above (p_0) can be set equal to the pressure of the 10m and the surface of the water, plus (+) the weight of the next 10m (pgh). Thanks for the reality check!