$A$ steady flow of water passes along a horizontal tube from a wide section $X$ to the narrower section $Y$,see figure. Manometers are placed at $P$ and $Q$ at the sections. Which of the statements $A, B, C, D$ is most correct?

What type of fluid can be applied in Bernoulli's equation?

Water is flowing through a horizontal tube having cross-sectional areas of its two ends as $A$ and $A'$ such that the ratio $A/A'$ is $5$. If the pressure difference of water between the two ends is $3 \times 10^5 \, N \, m^{-2}$,the velocity of water with which it enters the tube will be ......... $m \, s^{-1}$ (neglect gravity effects).

An ideal fluid of density $800 \; kg \cdot m^{-3}$ flows smoothly through a bent pipe (as shown in the figure) that tapers in cross-sectional area from $a$ to $\frac{a}{2}$. The pressure difference between the wide and narrow sections of the pipe is $4100 \; Pa$. At the wider section,the velocity of the fluid is $\frac{\sqrt{x}}{6} \; m \cdot s^{-1}$. Find the value of $x$. (Given $g = 10 \; m \cdot s^{-2}$)

$A$ train with cross-sectional area $S_t$ is moving with speed $v_t$ inside a long tunnel of cross-sectional area $S_0$ $(S_0 = 4S_t)$. Assume that almost all the air (density $\rho$) in front of the train flows back between its sides and the walls of the tunnel. Also,the air flow with respect to the train is steady and laminar. Take the ambient pressure and that inside the train to be $p_0$. If the pressure in the region between the sides of the train and the tunnel walls is $p$,then $p_0 - p = \frac{7}{2N} \rho v_t^2$. The value of $N$ is. . . . .

$A$ steady flow of a liquid of density $\rho$ is shown in the figure. At point $1$,the area of cross-section is $2A$ and the speed of flow of liquid is $\sqrt{2} \ m \ s^{-1}$. At point $2$,the area of cross-section is $A$. Between the points $1$ and $2$,the pressure difference is $100 \ N \ m^{-2}$ and the height difference is $10 \ cm$. The value of $\rho$ is (Acceleration due to gravity $= 10 \ m \ s^{-2}$) (in $kg \ m^{-3}$)