Pressure at the bottom of a tank of water is $3P$, where $P$ is atmospheric pressure. If water is drawn out till the level of water is lowered by one fifth, then the pressure at the bottom of the tank is
A$2P$
B$13P/5$
C$8P/5$
D$4P/5$
Medium
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B$13P/5$
b $3 P=P+h \rho_{w} g \Rightarrow h \rho_{w} g=2 P$
when water is drawn out, the pressure at bottom.
$P^{\prime}=P+\left(h-\frac{h}{5}\right) \rho_{w} g=P+\frac{4}{5} h \rho_{w} g$
$P^{\prime}=P+\frac{4}{5}(2 P)=\frac{13}{5} P$
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