Question

A spring balance A reads $2kg$ when a block of mass m suspended from it. Another balance B reads $5kg$ 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 $2kg$ and B will read between $5kg$ and $5kg$.
• 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 $2kg$ and B will read between $5kg$ and $5kg$.

Due to displacement of water in the beaker caused by the mass, the mass experiences an upward buoyant force, less in magnitude than the weight of body. Hence the weight read by balance A is lesser than $2kg$.

Also a reaction pair force of the buoyant force on mass acts on water downwards. Hence this force$(<2kg)$ adds to the weight of water, and the reading of balance B is between $3kg$ and $5kg$.