Question

Why is the dam of the water reservoir thick at the bottom?
A) Quantity of water increases with depth
B) Density of water increases with depth
C) Pressure of water increases with depth
D) Temperature of water increases with depth

Answer 1

Hint: At the bottom of the tank or reservoir the pressure of water is much higher than at the top. This is the reason generally the outlet of the dam reservoir is made slightly at the lower part of the reservoir.
Pressure of the water is given by:
$P = \rho gh$ (P is the pressure, g is the acceleration due to gravity, h is the height, $\rho $ is the density)
We will use the above mentioned concept to prove that the pressure of the water increases with depth.

Complete step by step solution:
First we will make use of the formula to understand the concept and then we will cite an example to prove that the pressure of water increases at the bottom of the reservoir.
$P = \rho gh$ ($\rho $ and g are the constant quantities)
h is the variable quantity which increases as we go deep down the reservoir and pressure is directly proportional to the h height.
Therefore, we can conclude that pressure increases on going deep down the reservoir.
Now, we will make use of an experiment to understand the problem better.
We take a drum full of water and make three holes in it. One hole is made just above the bottom one at the middle and one nearby the top of the drum. We will check the intensities of water coming out of the three holes. Hole at the bottom will give the maximum discharge of the water middle one at little less than the bottom one and the hole at the top has very less discharge of the water due to the fact that pressure of the water increases with depth.

This is the reason reservoir walls are made thicker at the bottom to bear maximum pressure and to avoid breaching of the reservoir.

Option (C) is correct.

Note: We can also understand the above problem with the triangle approach of decreasing pressure at the top and pressure is maximum at the bottom as the shape of the triangle is, the pressure goes on increasing as we move down and decreases as we go up.