Above water surface

If we remove the stone from the water, we apply a force of 120N. How much force will we exert if we move the stone above the water? The stone's density is 5000 kg/m³.

Correct answer:

F₂ =  150 N

Step-by-step explanation:

$$\begin{gathered} F_1=120\text{N} \\ g=10{\text{m/s}}^2 \\ {\rho }_1=5000{\text{kg/m}}^3 \\ {\rho }_2=1000{\text{kg/m}}^3 \\ m=\rho \cdot V \\ F=m\cdot g \\ {F}_1={\rho }_1\cdot V\cdot g-{\rho }_2\cdot V\cdot g \\ V=\frac{F_1}{g\cdot ({\rho }_1-{\rho }_2)}=\frac{120}{10\cdot (5000-1000)}=\frac{3}{1000}=0.003{\text{m}}^3 \\ {F}_2={\rho }_1\cdot V\cdot g=5000\cdot 0.003\cdot 10=150\text{N} \end{gathered}$$

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