Question

A spring balance A reads $2kg$ with a block of mass $m$ suspended from it. Another balance Breads $5kg$ 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. In this situation.

• A. The balance A will read $2kg$
• B. The balance B will read $5kg$
• C. The balance A will read less than $2kg$
• D. The balance $A$ and $B$ will.read $2kg$ and $5kg$.

Answer 1

The correct option is C The balance A will read less than $2kg$

As the block $m$ is immersed in the liquid, a force of buoyancy acts on it in the upward direction and hence, the apparent weight of the block as shown by the balance A will be less than $2kg$.
Moreover, as the liquid in the beaker exerts an upward force on the mass m, the mass m exerts an equal force on the liquid in the downward direction, according to Newton's law. Hence, the balance B will read more than $3kg$ up to $5kg$.
Hence, the balance A will read less than $2kg$ and B will read between $3kg$ and $5kg$.