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Fluids problem-elementary

  • Thread starter Moe*
  • Start date
10
0
1. Homework Statement

THe human lungs can operate w a pressure differential of abt 1/20 of an atmosphere. If a diver uses a snorkle for breathing, about how far below the water level can they swim?

2. Homework Equations

P=P(i) + pgh

where p is ro, density.

3. The Attempt at a Solution

1026kPa=101.3kPa + (0.001g/l)(9.8m/s^2)(h)

I isolated for h, but the number i get is way larger than the diameter of earth.

My problem is this: the units don't seemt o cancel out properly. the units for height work out to be L/m^2
 

Answers and Replies

412
2
You are not using a proper set of units here. Use the S.I system throughout. For pressure, use Pascals (Pa), not kPa. 1 Pa = 1 N/m² . For density, use kg/m³. Density of water is: 1000 kg/m³. You have used the right units for gravitational acceleration and your 'h' should come out in meters.

You have used the density of water as 0.001 g/l. It is actually 1000 g/l. [or 1000 kg/m³].

As for the unit dimensions, you are getting it as L/m². 'L' is litres, so it has the dimension, [Length]³, and the denominator has dimension, [Length]². When it cancels out, you get the height's dimensions as [Length].. so there is no error in the dimensional analysis.
 

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