Mechanical Properties of Fluids - Result Question 8
8. A wind with speed $40 m / s$ blows parallel to the roof of a house. The area of the roof is $250 m^{2}$. Assuming that the pressure inside the house is atmosphere pressure, the force exterted by the wind on the roof and the direction of the force will be $(\rho _{\text{air }}=1.2 kg / m^{3})$
[2015]
(a) $4.8 \times 10^{5} N$, upwards
(b) $2.4 \times 10^{5} N$, upwards
(c) $2.4 \times 10^{5} N$, downwards
(d) $4.8 \times 10^{5} N$, downwards
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Answer:
Correct Answer: 8. (b)
Solution:
- (b) According to Bernoulli’s theorem,
$P+ _2^{1} \rho v^{2}=P_0+0$
So, $\Delta P=\frac{1}{2} \rho v^{2}$
$F=\Delta PA=\frac{1}{2} \rho v^{2} A$
$=\frac{1}{2} \times 1.2 \times 40 \times 40 \times 250$
$=2.4 \times 10^{5} N$ (upwards)
