Question

A beaker containing water is placed on the platform of a spring balance. The balance reads $1.5kg$. A stone of mass $0.5kg$ and density $500kg/m^3$ is completely immersed in water without touching the walls of beaker. What will be the balance reading now?

• A. $2kg$
• B. $2.5kg$
• C. $1kg$
• D. $3kg$

Answer 1

The correct option is A $2kg$

If we consider beaker, water and stone as a system, net force is just the weight of beaker, water and stone. Since as the water exerts upthrust on the stone, the stones also exerts force of same amount downwards according to Newton's third law of motion. these forces cancel out. Therefor spring balance will now show the reading of $1.5+0.5kg=2kg$.