The pressure at the bottom of a tank of water is $3P$,where $P$ is the atmospheric pressure. If the water is drawn out until the level of water is lowered by one-fifth,the pressure at the bottom of the tank will now be:

Explain why:
$(a)$ The blood pressure in humans is greater at the feet than at the brain.
$(b)$ Atmospheric pressure at a height of about $6 \; km$ decreases to nearly half of its value at sea level,though the height of the atmosphere is more than $100 \; km$.
$(c)$ Hydrostatic pressure is a scalar quantity even though pressure is force divided by area.

An open $U$-tube contains mercury. When $13.6 \,cm$ of water is poured into one of the arms of the tube,then the mercury rise in the other arm from its initial level is ....... $cm$

Define density. Write its unit and dimensional formula.

$A$ triangular lamina of area $A$ and height $h$ is immersed in a liquid of density $\rho$ in a vertical plane with its base on the surface of the liquid. The thrust on the lamina is

$A$ cylindrical vessel of base radius $R$ and height $H$ has a narrow neck of height $h$ and radius $r$ at one end (see figure). The vessel is filled with water (density $\rho_w$) and its neck is filled with immiscible oil (density $\rho_0$). Then,the pressure at