Question

A wooden block of volume 1000 cm³ 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. (a) 10 N
• A. (b) 9 N
• A. (c) 8 N
• A. (d) 7 N

Answer 1

(d)

Reading of the spring balance = Apparent weight of the block

= Actual weight – upthrust

$= 12 - V_{in}\sigma g$

$= 12 - 500 \times 10^{- 6} \times 10^{3} \times 10 = 12 - 5 = 7N.$