The cube is in equilibrium under three forces as, spring force kx, where x = elongation of the spring,
Gravitational force ω, weight of the cube = mg
Buoyant force,
Fb (or upward thrust) imparted by the liquid on the cube given as
Fb =
Vdg , where V = volume of the immersed portion of the cube.
For complete immersion, V = volume ofthe cube
For equilibrium of the cube
kx +
Fb = mg
⇒ x =
=
where, V =
() ⇒ x =
(1−)