Question

A copper 20cm on a side is completely submerged underwater. Calculate the buoyant force acting on the cube?

a.58.7 N b. 75.8 N c. 78.5 N d. 87.5 N

Answer 1

The volume of the cube is $V = l^3 = (0.2 m)^3 = 0.008 m^3$.

Buoyant force, acting on it is $F = \rho g V$, where $\rho$ is the density of water, $g$ is gravitational acceleration and $V$ is the submerged volume.

Hence, $F = 1000 \frac{kg}{m^3} \cdot 9.81 \frac{m}{s^2} \cdot 0.008 m^3 \approx 78.5 N$, so the answer is c).