Question

A block of volume V and of density ${\sigma }_0$ is placed in liquid of density ${\sigma }_1({\sigma }_1>{\sigma }_b)$, then block is moved upward upto a height h and it is still in liquid. The increase in gravitational potential energy of the block is

• A. ${\sigma }_b$ Vgh
• B. $({\sigma }_b+{\sigma }_1)$ Vgh
• C. $({\sigma }_b-{\sigma }_1)$ Vgh
• D. None of these

Answer 1

The correct option is A ${\sigma }_b$ Vgh

The increase in gravitational potential energy of the block will be independent of density of liquid or displacement of liquid by motion of block because it is :increase in gravitational potential energy "of the block".
mass$=$density$\times$volume
increase in gravitational potential energy of the block $=mgh=V\times {\sigma }_b\times gh={\sigma }_{b}Vgh$