Q. 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 decrease in tension in the string after immersion is
A) $9.8\ N$
B) $6.2\ N$
C) $3.6\ N$
D) $1.0\ N$
Explanation
(c) Here, mass of block, $m = 1kg$
Volume of a block, $V = 3.6 \times 10^{- 4}m^{3}$
Tension in the string, $T = mg = mg - V\rho_{water}g$
$\therefore$ Decrease in the tension of string $= T - T$
$= mg - \left\lbrack mg - V\rho_{water}g \right\rbrack = V\rho_{water}g$
$= \left( 3.6 \times 10^{- 4}m^{3} \right) \times \left( 10^{3}kgm^{- 3} \right) \times \left( 10ms^{- 2} \right) = 3.6\ N$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.