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Pressure of fluids – problems and solutions

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1.

Pressure of fluids – problems and solutions 1

Acceleration due to gravity is 10 N/kg. The surface area of fish pressed by the water above it is 6 cm2. Determine the force of water above fish that acts on fish.

Known :

Acceleration due to gravity (g) = 10 N/kg

Surface area of fish (A) = 6 cm2 = 6 x 10-4 m2

Density of water = 1 gram/cm3 = 1 (10-3 kg) / 10-6 m3 = 103 kg/m3 = 1000 kg/m3

Height of water = 100 cm – 15 cm = 85 cm = 85 x 10-2 meters

Wanted : Force of the water above fish that acts on fish

Solution :

Equation of pressure:

P = F / A

F = P A

F = ρ g h A

F = (1000)(10)(85 x 10-2)(6 x 10-4 m2)

F = (104)(510 x 10-6)

F = 510 x 10-2

F = 5.1 Newton

2. The normal pressure of blood is 80 mm hg to 120 mm hg. This value is equal to…

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A. 80 Pascal to 120 Pascal

B. 800 Pascal to 1200 Pascal

C. 10256 Pascal to 17589 Pascal

D. 10526 Pascal to 15789 Pascal

Known :

The normal pressure of blood = 80 mm Hg – 120 mm Hg

Wanted: This value is equal to… Pascal

Solution :

The height of mercury in a barometer (above the surface of the sea) = 760 mm Hg

Pressure of air (above the surface of sea) = 1 atm = 1.0 x 105 Pascal

1 mm Hg = ……. Pascal?

Pressure of fluids – problems and solutions 2

80 mm Hg = 80 x 131.58 Pascal = 10,526 Pascal

120 mm Hg = 120 x 131.58 Pascal = 15,789 Pascal

The correct answer is D.

3. Above the surface of the sea, the height of mercury in a barometer is 760 mm. If at a place, the height of mercury in a barometer is 700 mm. Determine the pressure of air at that place.

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Known :

The height of mercury in a barometer (above the surface of the sea) = 760 mm Hg

Pressure of air (above the surface of sea) = 1 atm = 1,013 x 105 Pascal

Wanted: Determine the pressure of air if the height of mercury is 700 mm

Solution :

760 mm Hg = 1.013 x 105 Pascal

700 mm Hg = ……… Pascal?

Pressure of fluids – problems and solutions 3

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