Suppose the glass

(a) Here, we are removing the atmospheric pressure.

Hence, pressure at the bottom of the glass,

Therefore, the downward force is given by .

For the second case, the vertical force is equal to the weight of the water,

The horizontal forces again cancel out. So the total upward force is,

The total force on the bottom depends only on the height of the vessel, the bottom area and the weight of the water. As density of water is fixed, the total force thus depends on the volume of the container. These quantities can remain same for different shapes and hence the answers do not depend on the shape of the container.