# physics

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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!

• physics -

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?

• physics -

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