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

At every point of a liquid at rest,the tangential stress is zero. Explain with reason.

$A$ cubical block of wood, of length $10 \,cm$, floats at the interface between oil of density $800 \,kg/m^3$ and water. The lower surface of the block is $1.5 \,cm$ below the interface. If the depth of water is $10 \,cm$ below the interface and oil is up to $10 \,cm$ above the interface, then the difference in pressure at the lower and the upper face of the wooden block is:
(Assume density of water, $\rho_w = 1000 \,kg/m^3$ and acceleration due to gravity, $g = 10 \,m/s^2$) (in $\,Pa$)

$A$ $U$ tube with both ends open to the atmosphere is partially filled with water. Oil,which is immiscible with water,is poured into one side until it stands at a distance of $10\, mm$ above the water level on the other side. Meanwhile,the water rises by $65\, mm$ from its original level (see diagram). The density of the oil is ......... $kg/m^3$.

In a $U-$tube experiment,a column $AB$ of water is balanced by a column $CD$ of oil,as shown in the figure. Then the relative density of oil is

Three different liquids are filled in a $U$-tube as shown in the figure. Their densities are $\rho_1, \rho_2$ and $\rho_3$ respectively. From the figure, we may conclude that: