A 180-km/h wind blowing over the flat roof of a house causes the roof to lift off the house.?

If the house is 6.8 m × 12.6 m in size, estimate the weight of the roof. Assume the roof is not nailed down.

Answer 1

The weight must equal the lift force:
F = ½*ρ*v²*A*C

180km/h * 1m/s / 3.6km/h = 50 m/s
and taking the density of air as 1.27 kg/m³
and lift coefficient C = 1 gives us
F = ½ * 1.27kg/m³ * (50m/s)² * 6.8m * 12.6m * 1 = 1.36e5 N

Hope this helps!

Answer 2

d = air density = 1.184 kg/m3 at 25C
F =(1/2)(d)(v^2)(A)
F =(1/2)(1.184)(50^2)(6.8*12.6)
F = 126 806 N <===ans

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