physics
posted by Nikki .
I'm having a really hard time with this physics problem...not really sure where to begin or which equation to use....please help:
You are assigned the design of a cylindrical, pressurized water tank for a future colony on Mars, where the acceleration due to gravity is 3.71 meters per second per second. The pressure at the surface of the water will be 100 kPa , and the depth of the water will be 13.9m . The pressure of the air in the building outside the tank will be 85.0 kPa .
Find the net downward force (in newtons) on the tank's flat bottom, of area 2.30 , exerted by the water and air inside the tank and the air outside the tank.
Any help would be much appreciated! Thank you!

The "pressure at the surface of the water", what is above the water? Air at 100kPa? So, is this gauge pressure in relation to ouside the tank, or absolute pressure?

I believe he pressure on the surface is the controlled gauge pressure in the tank in relation to the outside.