Which of the following functions of $A$ and $B$ may be performed if $A$ and $B$ possess different dimensions

The area of cross section of the wides tube shown in the figure is $800\,cm^2$. If a mass of $12\,kg$ is placed on the massless piston, the difference in the heights $h$ in the level of water in two tubes ........ $m$

Horizontal tube of non-uniform cross-section has radius of $0.2\,m$ and $0.1\,m$ respectively at $P$ and $Q$. For streamline flow of liquid, the rate of liquid flow

In making an alloy, a substance of specific gravity $s_1$ and mass $m_1$ is mixed with another substance of specific gravity $s_2$ and mass $m_2$ then the specific gravity of the alloy is

A spherical body of mass $m$ and radius $r$ is allowed to fall in a medium of viscosity $\eta $. The time in which the velocity of the body increases from zero to $0.63\, times$ the terminal velocity $(v)$ is called time constant $\left( \tau  \right)$. Dimensionally $\tau $ can be represented by

A cylindrical vessel filled with water upto the height $H$ becomes empty in time $t_0$ due to a small hole at the bottom of the vessel. If water is filled to a height $4H$ it will flow out in time