Question

A boy has $60\, kg$ weight. He wants to swim in a river with the help of a wooden log. If relative density of wood is $0.6$. What is the minimum volume of wooden log? (Density of river water is $1000\, kg / m ^{3}$ )

• A. $0.66\,m^{3}$
• B. $150\,m^{3}$
• C. $\frac{3}{1}\,m^{3}$
• D. $\frac{3}{20}\,m^{3}$

Answer 1

Answer: (D)

$\frac{3}{20}\,m^{3}$

Answer 2

From Archimedes principle Weight of (boy + log) = weight of water displaced $(60+V \times 0.6 \times 10^{3})g=V \times 10^{3} g$
$\Rightarrow 0.4 \times 10^{3}V=60$
$\Rightarrow V=\frac{60}{0.4 \times 10^{3}}=\frac{600}{400}=\frac{3}{20}m^{3}$