Question

Three identical blocks each of mass $m=1kg$ and volume $3\times {10}^{-4}{m}^3$ are suspended by massless strings from a support as shown. Underneath are three identical containers containing the same amount of water that are placed over the scales. In fig (a), the block is completely out of the water; in fig (b), the block is completely submerged but not touching the beaker and in fig (c), the block rests on the bottom on the beaker. The scale in fig (a) reads 14 N

• A. the tension in the string in (b) is 10 N
• B. the tension in the string in (b) is 7 N
• C. the reading of the scale in (b) is 17 N
• D. the reading of the scale in (c) is 24 N

Answer 1

Answer: (B), (C), (D)

the reading of the scale in (b) is 17 N
the tension in the string in (b) is 7 N
the reading of the scale in (c) is 24 N

In figure (b), buoyant acting on the block=$V\rho g=3\times {10}^{-4}\times {10}^3\times 10N=3N$

Forces acting on the block balance, thus $mg=B+T$

$⟹T=mg-B=10N-3N=7N$

Reading on the scale-Weight of the water+Buoyant force's reaction downwards

$=14N+3N=17N$

In figure (c), reading of the scale=Weight of water+weight of block

$=14N+10N=24N$