A hurricane wind blows across a 7.10 15.1 flat roof at a speed of 130 . A. Is th

Question

A hurricane wind blows across a 7.10 15.1 flat roof at a speed of 130 . A. Is the air pressure above the roof higher or lower than the pressure inside the house? Explain. B. What is the pressure difference? C. How much force is exerted on the roof?

Explanation / Answer

1) density of freshwater: ? = 1000 kg/m³ density of seawater: ?s = 1025 kg/m³ specific gravity: ? = ?s/? = 1.025 = W/Fb=> wgt in air/buoyant force displaced vol.of seawater: Vdisplaced = 3*20*0.8.= 48 m³ buoyant force of seawater: Fb = ?sVg = 1025*48*9.81 = 482,652 N barges’ wgt in air: W = 482652*1.025 = 494,718 N buoyant force of freshwater: Fb’ Fb’ = ?Vg = 1000*3*20*d*9.81 = W/? = 494718/1.025 draught in freshwater: d = (494718/1.025)/ 1000*3*20*9.81 = 0.82 m Therefore, the cargo barge will sit 2 cm deeper in the river. 2) Employ Bernouliis' eqn: p + ½ ?v² = p’ + ½ ?v’² 101.3 kPa = p’ + ½ 1.29 *130²x106/3600² p’ = 101.3x10³ - 0.841x10³ = 100.4 kPa Therefore the pressure is lower on the roof. ?p = 101.3 – 100.4 = 0.841 kPa F = ?p/A = 0.841/15*6 = 9.34 N 3) Conservation of energy: ½ mv² = mg(50) v = v2g(50) = 10v9.81 =31.3 cm/s Q = dV/dt = vA =31.3p(3²/4)(10-³)² = 221x10-6 = 0.0221 cm³/s

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