Question

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

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

Answer 1

Answer: (A)

Volume of cork $ =\frac{4}{0.2\times {{10}^{3}}}{{m}^{3}} $
Weight of liquid displaced when cork is fully immersed in water
$ =\frac{4}{200}\times 1.03\times {{10}^{3}}\times 9.8\,N $
Lifting force
$ =\frac{4}{200}\times 1.03\times {{10}^{3}}\times 9.8-4\times 9.8 $
$ =201.88-39.2 $
$ =163\,N $