Question

Air of density $1.3kg{m}^{-3}$ blows horizontally with a speed of $108km{h}^{-1}$. A house has a plane roof of area $40m^2$. The magnitude of aerodynamic lift on the roof is.

• A. $2.34\times {10}^4$ Dynes
• B. $0.234\times {10}^{4}N$
• C. $2.34\times {10}^{4}N$
• D. $23.4\times {10}^{4}N$

Answer 1

The correct option is C $2.34\times {10}^{4}N$

Applying bernoullis theorem above and below the roof,
$p_1+\frac{1}{2}+v_1^2=p_2$
$\Rightarrow p_2-p_1=\frac{1}{2}+v_1^2=\frac{1}{2}\times 1.3\times {\left(30\right)}^2$
$\Rightarrow$ difference in pressure $=585N/m^2...........2$
So,
Magnitude of aerodynamic life$=1\times Area$
$=585\frac{N}{m^2}\times 40m^2$
$2.34\times {10}^{4}N$