Posted by Catie on Monday, August 15, 2011 at 12:11am.
A hurricane wind blows across a 6.00 m times 15.0 m flat roof at a speed of 190 km/hr.
What is the pressure difference? Use 1.28 kg/m^3 for the density of air.
How much force is exerted on the roof?
If the roof cannot withstand this much force, will it "blow in" or "blow out"?
Math - MathMate, Monday, August 15, 2011 at 9:58am
Use Bernoulli's equation:
P1+ρgh1+(1/2)ρv1² = P2+ρgh2+(1/2)ρv2²
v1=exterior wind velocity
v2=interior wind velocity = 0
h1-h2 is the negligible height differences
ρ=density of air (1.293 kg-m^-3)
which by neglecting ρg(h2-h1), and substituting v1=0 we get
Suction force (blows out):
The above calculation of pressure assumes:
1. the pressure factor is -1 (which is not far for a flat roof).
(Broken Link Removed)
2. the STP value of ρ=1.293kg/m³ instead of 1.28 as stipulated. You will need to make adjustments to get the correct answer.
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