Question

Equal volume of two liquids of densities ρ1 and ρ2 are poured into two identical cuboidal beakers. The hydrostatic forces on the respective vertical face of the beakers are F1 and F2 respectively. If ρ1 > ρ2, which one will be the correct relation between F1 and F2?

(a) F1 > F2

(b) F1 ≥ F2

(c) F1 < F2

(d) F1 ≤ F2

The question was posed to me in an interview.

The above asked question is from Hydrostatic Force on Plane Area in section Hydrostatic Forces on Surfaces of Fluid Mechanics

Answer 1

Right answer is (a) F1 > F2

For explanation: Hydrostatic force per unit width on a vertical side of a beaker = ^1 ⁄ 2 * ρgh^2, where ρ = density of the liquid and h= height of liquid column. Thus if ρ1 > ρ2, F1 > F2 and F1 ≠ F2, when the h is constant.