Question

A spring balance $A$ reads $2 kg$ with a block of mass $m$ suspended from it. Another balance $B$ reads $3 kg$ when a beaker with a liquid is put on its pan. The two balances are now so arranged that the hanging mass $m$ is fully immersed inside the liquid in the beaker as shown in the figure given below.

In this situation,

• A. the balance A will read 2 kg and B will read 5 kg
• B. the balance A will read 2 kg and B will read 3 kg
• C. the balance A will read less than 2 kg and B will read between 3 kg and 5 kg
• D. the balance A will read less than 2 kg and B will read 3 kg

Answer 1

Answer: (C)

When block is dipped in water, it displaces some water which exerts buoyant force on block. As a result, reading on scale $A$ will be lower than $2\, kg$. Due to reaction of block (which is equal to buoyant force), beaker of water is pushed. So, reading of scale $B$ will be more than $3\, kg$.