physics question?

Question

A container is filled with water to a depth of 20.0 cm. On top of the water floats a 30.0cm thick layer of oil with a density of .70 X 10^3 kb/m^3.

a. what is the pressure at the surface of the water?

b. what is the absolute pressure at the bottom of the container

If anyone could show me how to get the answers to this question i would greatly appreciate it. Thanks.

Answer 1

p - pressure
r - density
g - gravitational acc. (~=10)
h - height.

surface of water only presure is by the oil.

p = hrg
30 cm = 0.3m
p = (0.3)(0.7*10^3)(10)
= 2100 Pa

pressure by at bottom of the container is the sum of pressure by oil and water

pressure by water = (0.2)(1000)(10)
= 2000 Pa

sum of presure is = 2000 + 2100
= 4100

it would be good if you include atmospheric pressure. which is ~101 kPa.

Answer 2

I assume that kb is kg.
Normalized that would be 700 kg/m^3.
At the bottom of the oil:
0.300 * 700 * 9.6 = 2016.0 pascals.
At the bottom of the water:
0.200 * 1000 * 9.6 + 2016.0 = 3936.0 pascals.
lilmaninbigpants has a good point about including atmospheric pressure as well.
3936.0 + 101325 = 105261 pascals.

Answer 3

Atmospheric pressure = 1 bar/10m of water.

a...30cm = 0.03bar
.....0.030 x 0.7 = 0.021bar

b...20cm = 0.020bar

Total absolute pressure = 1.041 bar.