Question

A block of aluminium of mass $1 \,kg$ and volume $3.6 \times 10^{-4} \,m ^{3}$ is suspended from a string and then completely immersed in a container of water. The decrese in tension in a container of water. The decrease in tension in the string after immersion is

• A. 9.8 N
• B. 6.2 N
• C. 3.6 N
• D. 1.0 N

Answer 1

Answer: (C)

Here, mass of block $=m=1 \,kg$
Volume of the block, $V=3.6 \times 10^{-4} \,m ^{3}$
Tension in the string, $T=m g=m g-V \rho_{\text {water }} g$
$\therefore $ Decrease in the tension of string
$T-T^{'} =m g-\left[m g-v \rho_{\text {water }} g\right]=V \rho_{\text {water }} g $
$=3.6 \times 10^{-4}\, m ^{3} \times 10^{3} \,kgm ^{-3} \times 10\, ms ^{-2}=3.6\, N$