Your dorm has an amateur hour every Friday night. Since you have a tremendous lu
ID: 1261617 • Letter: Y
Question
Your dorm has an amateur hour every Friday night. Since you have a tremendous lung capacity, you challenge everyone to a lung capacity competition which is conducted by blowing air through one straw which in turn pulls water up through another straw, as shown in the figure. The straws are identical and have a diameter of 0.92 cm, you are able to exhale 1.1 liters of air through the horizontal straw in as little as 2 seconds, and the density of air is 1.29 kg/m3. Determine the following.
(a) speed of the air as it travels through the horizontal straw
m/s
(b) height to which water rises in the vertical straw
cm
Explanation / Answer
a) 1.1L = 1100 cm^3
1100 cm^3 = 1100cm^3 x 10-6 (m^3 / cm^3) = 1.1 x 10^-3 m^3
Volume of air flow = 1.1 x 10-3 / 2 = 5.5 x 10^-4 m^3/s
Area of Straw = pi x r^2
A = pi x (0.0092 /2)^2 = 0.665 x 10^-4 m^2
Speed of air through straw = Air flow volume per sec / Area
= 5.5 x 10-4 / (0.665 x 10-4) = 8.27 m/s
B) Pressure Drop = density x v^2 / 2
= 1.29 x (8.27)^2 / 2
= 44.15 Pa
1 Pa = 0.010197 cm of water
44.15 Pa = 0.010198 x 44.15 = 0.450 cm .....Ans
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