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9-1.Fluid Mechanics
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Water coming out of a horizontal tube at a speed ? strikes normally a vertically wall close to the mouth of the tube and falls down vertically after impact. When the speed of water is increased to $2v$ .
A
the thrust exerted by the water on the wall will be doubled
B
the thrust exerted by the water on the wall will be four times
C
the energy lost per second by water striking the wall be increased eight times.
D
$B$ and $C$ both
Solution
Thrust $=$ Rate of charge of linear momentum
Thrust $=\mathrm{mv}$ where $\mathrm{m}$ is mass striking per sec.
$=\rho a v \times v \Rightarrow \quad$ Thrust $=\rho a v^{2}$
Energy lost for second $=\frac{1}{2} m v^{2}=\frac{1}{2} \rho a v . v^{2}=\frac{1}{2} \rho a v^{3}$
so option $(\mathrm{B}, \mathrm{C})$ are correct.
Standard 11
Physics
