Question

Figure shows a weigh-bridge, with a beaker $P$ with water on one pan and a balancing weight $R$ on the other. a solid ball $Q$ is hanging with a thread outside water. It has volume $40c{m}^3$ and weighs $80g$. If the solid is lowered to sink fully in water, but not touching the beaker anywhere, the balancing weight ${}^{\prime }{R}^{\prime }$ will be

• A. same as $R$
• B. $40g$ less than $R$
• C. $40g$ more than $R$
• D. $80g$ more than $R$

Answer 1

The correct option is C $40g$ more than $R$

Buoyancy force on sphere will B=$40\times 1\times g$

Now thrust due to this buoyancy on water is $B$ or

Mass increased due to this thrust is $m=B/g=40g$.

Now the balancing weight will be $40g$ more than R , remaining weight of sphere is supported by tension .