Q. A wooden block of volume $1000\ cm^{3}$ is suspended from a spring balance. It weighs $12\ N$ in air. It is suspended in water such that half of the block is below the surface of water. The reading of the spring balance is
A) $10\ N$
B) $9\ N$
C) $8\ N$
D) $7\ N$
Explanation
(d) Reading of the spring balance
$=$ Apparent weight of the block
= Actual weight – upthrust
$= 12 - V_{in}\sigma g$
$= 12 - 500 \times 10^{- 6} \times 10^{3} \times 10 = 12 - 5 = 7N$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.