# MCAT Physics Question — Water Pressure

• Reviewed By: Liz Flagge
• A holding tank at sea level (atmospheric pressure 1.01 x 105 Pa) containing water has a pressure of 2 x 105 Pa at 10 m depth. What is the pressure in an equivalent holding tank containing mercury (specific gravity = 13) at 1 m depth in Denver, CO (atmospheric pressure 8.4 x 104 Pa)?

A. 2 x 105 Pa

B. 1 x 105 Pa

C. 1.4 x 106 Pa

D. 8.4 x 104 Pa

Formula for hydrostatic pressure in a fluid:

Ptot = P0 + ρgh

##### Click for Explanation

Here, we can simply plug in the values provided:

Ptot = (8.4 x 104) + (13,000 kg/m3 x 10m/s2 x 1m) = 2.14 x 105 Pa

A. 2 x 105 Pa correct, matches our calculation

B. 1 x 105 Pa, incorrect, this is the same pressure at sea level for 10m of water, ignores fluid change and atmospheric pressure change

C. 1.4 x 106 Pa, incorrect, this answer fails to change the fluid depth to 1m for the mercury rather than the 10m depth used for water

D. 8.4 x 104 Pa, incorrect, this answer ignores the fluid contribution to pressure and only uses the atmospheric contribution

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