fluids-flow rate, continuity

[missdoc92120]

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I'm having some trouble understanding this problem. It was a passage question. f=Av would bee used but why multiply by density of air?

If the speed of the air flowing through the cylinder is found to be 15 m/s, what is the mass of the air moving past any point in the cylinder each second?

The area is .005m^2 and density of air is 1.2 kg/m^3

The answer is 90 grams.

 

[FeinMS]

volume flow rate is expressed in (volume/second.) To find the mass of the air moving past any point in the cylinder each second, you're looking for (mass/second.) Since density=mass/volume, you should use density to convert volume to mass.

 

[missdoc92120]

Thanks! That makes sense.