MCAT Physics Question — Pressure
 by
 Dec 31, 2014
 MCAT Blog, MCAT Physics, MCAT Question of the Day
At a depth of 5 meters, the pressure in a tank of water is equal to 1.5 atm. What is the pressure at a depth of 20 meters?
A) 3 atm
B) 4 atm
C) 5 atm
D) 6 atm
Explanation
This question is testing your understanding of the relationship between total pressure, atmospheric pressure, and gauge pressure: P_{total }= P_{atm }+ P_{gauge}. To begin, you must know that P_{atm }results from the pressure of the atmosphere and P_{gauge} results from the pressure due to the fluid. To calculate the gauge pressure, you can use the equation P_{gauge }= rgd, where r is the density of the fluid, g is gravity, and d is the depth below the surface of the fluid.
At a depth of 5 meters, P_{gauge }= rgd = (1000 kg/m^{3})(10 m/s^{2})(5 m) = 50,000 N/m^{2} or ~0.5 atm. Therefore, the P_{atm }is equal to 1 atm. Thus, at a depth of 20 m, P_{total }= P_{atm }+ P_{gauge} = 1 atm+ (1000 kg/m^{3})(10 m/s^{2})(20 m) = 3 atm, making A the correct answer.
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