MCAT Physics Question 59: Answer and Explanation

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Question: 59

14. Two fluids, A and B, have densities of x and 2x, respectively. They are tested independently to assess absolute pressure at varying depths. At what depths will the pressure below the surface of these two fluids be equal?

  • A. Whenever the depth of fluid A is one-half that of fluid B
  • B. Whenever the depth of fluid A equals that of fluid B
  • C. Whenever the depth of fluid A is 2 times that of fluid B
  • D. Whenever the depth of fluid A is 4 times that of fluid B

Correct Answer: C

Explanation:

The equation for absolute (hydrostatic) pressure is P = Po + ρgz, where Po is the pressure at the surface, ρ is the density of the fluid, g is acceleration due to gravity, and z is the depth in the fluid. If the density of fluid B is twice that of fluid A, then the depth in fluid A will have to be twice that in fluid B to obtain the same absolute pressure:

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