Topic: Fluids
Concepts: Buoyant force, Equivalence principle, Floating

Solution:

We initially balance the weight of the block with the buoyant force,

so the fraction submerged is given by

In the accelerating frame moving upward with $a$, the effective gravity is $g’=g+a$ since we include the fictitious inertial force $-m\vec{a}$. Thus, our force balance equation becomes

which yields the same fraction submerged $f_{\text{sub}}=\rho_{\text{obj}}/\rho_{\text{wat}}$. Thus, the block does not move in the liquid so the answer is C.