Question

A dam of water reservoir is built thicker at the bottom than at the top because:
A. Pressure of water is very large at the bottom due to its large depth
B. Water is likely to have more density at the bottom due to its large depth
C. Quantity of the water at the bottom is very large
D. None of the above

Answer 1

Hint: Make use of the concept that the pressure of the water increases with the increase in the depth of water (that is pressure is proportional to the depth).

Complete step by step solution:
As we all know that as we go deeper the pressure in the sea and oceans keeps on increasing, in the same way the pressure in the lower parts of the dam is higher than the top part of the dam, this is why dams are built thicker at the bottom than the top.
\[P=hpg\]
Where,
P = Pressure
h = Depth of the dam
g = acceleration due to gravity
Thus the dams are built thicker at the bottom in order to withstand the high pressure of water at the bottom of the dams.
So the correct answer would be (a) PRESSURE OF WATER IS VERY LARGE AT THE BOTTOM DUE TO ITS LARGE DEPTH.
The density of water remains the same from top to the bottom, no change in density will be seen in water at lower level or upper level depth.
The quantity of water will remain the same from top to bottom because in a dam the amount of water remains the same from top to bottom even when the water level in the dam rises.
So we can conclude that the pressure of water is always higher in the depth than at the top, this is the reason why the walls of the dam are constructed thicker at the bottom than the top.

Note: The pressure in the dam is higher at the bottom so in order to withstand that pressure the walls are built thicker at the bottom. Pressure is directly proportional to the depth of the dam.