A sealed tank containing seawater to a height of 10.7 m also contains air above the water at a gauge pressure of 3.20 atm. Water flows out from the bottom through a small hole. How fast is this water moving?

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Answer:

28.97 m/s

Explanation:

height of water (H1) = 10.7 m

Gauge pressure (Pg) = 3.2 x 1.01325 x 10^{5} = 324240 N/ m^[2}

pressure at the top (P1) = gauge pressure (Pg) + atmospheric pressure(Pa)  (Pg + Pa)

acceleration due to gravity (g) = 9.8 m/s^{2}

height at the bottom (H2) = 0

pressure at the bottom (P2) = atmospheric pressure = (Pa)

density of sea water (ρ) = 1030 kg/m^{3}

speed of water at the top (V1) = 0 (assuming the tank is big, the speed of water at any point on the surface is almost 0 and also the hole is very small compares to the size of the tank)

speed of water at the top (V2) = ?

applying Bernoulli's equation we can find the value of V2.

[tex]P1+pgh1+\frac{1}{2}pV1^{2}=P2+pgh2+\frac{1}{2}.pV2^{2}[/tex] (take note that [tex]p[/tex] represents ρ whcih is the density of sea water)

recall that P1 = Pg + Pa and P2 = Pa

[tex]Pg + Pa + pgh1 + \frac{1}{2}pV1^{2} = Pa + pgh2 + \frac{1}{2}.pV2^{2}[/tex]

[tex]Pg + pgh1 + \frac{1}{2}pV1^{2} = pgh2 + \frac{1}{2}pV2^{2}[/tex]

  • Gauge pressure (Pg) = 3.2 x 1.01325 x 10^{5} = 324240 N/ m^[2
  • substituting all required values into the equation above we have

[tex]324240 + (1030 x 9.8 x 10.7) + (\frac{1}{2}x1030x0^{2}) = (1030x9.8x0) + (\frac{1}{2}x1030xV2^{2}[/tex])

[tex]324240 + (1030 x 9.8 x 10.7) = (\frac{1}{2}x1030xV2^{2}[/tex])

V2 =

[tex]324240 + (1030 x 9.8 x 10.7) = \frac{1}{2}x1030xV2^{2}[/tex]

V2 = [tex]\sqrt{\frac{324240 + (1030 x 9.8 x 10.7)}{ \frac{1}{2}x1030}}[/tex]

V2 = 28.97 m/s

The water was moving out from the bottom at a velocity of 29 m/s

Applying Bernoulli's equation:

P + ρgh + (1/2)ρv² = constant

P is pressure, g is acceleration due to gravity, h is height, v is velocity, ρ is density.

At top:

P = 3.20 atm = 3.20 * 101300 Pa, ρ = 1025 kg/m³, v = 0, g = 9.81 m/s, h = 10.7 m, hence:

P + ρgh + (1/2)ρv² = ( 3.20 * 101300) + (1025 * 9.81 * 10.7) + 0

At bottom:

h = 0, P = 0

P + ρgh + (1/2)ρv² = 0 + 0 + (1/2* 1025)v²

Equating top and bottom:

( 3.20 * 101300) + (1025 * 9.81 * 10.7) = (1/2* 1025)v²

v = 29 m/s

The water was moving out from the bottom at a velocity of 29 m/s

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