Question

Find the lifting force of $4kg$ crock life belt in sea water, if the densities of crock and sea water are $0.2\times {10}^{3}kg/m^3$ and $1.03\times {10}^{3}kg/m^3$ respectively.

• A. $163N$
• B. $273N$
• C. $119N$
• D. $298N$

Answer 1

The correct option is A $163N$

Mass of crock life belt $m=4$ kg

Density of crock ${\rho }_c=0.2\times {10}^{3}kg/m^3$

Thus volume of crock life belt $V=\frac{m}{{\rho }_c}$

$\therefore$ $V=\frac{4}{0.2\times {10}^3}=2\times {10}^{-2}{m}^3$

Density of sea water ${\rho }_w=1.03\times {10}^{3}kg/m^3$

Lifting force required $F=B-W$

Or $F={\rho }_{w}Vg-{\rho }_{c}Vg=({\rho }_w-{\rho }_c)Vg$

$\therefore$ $F=(1.03-0.2)\times {10}^3\times 2\times {10}^{-2}\times 9.8$

$⟹$ $F=163$ N