Q1.The tension in a string holding a solid block below the surface of a liquid (of density greater than that of solid) as shown in the figure is T_o (To) when the system is at rest. What will be the tension in the string if the system has upward acceleration a.
(A) T_o\frac ag
(B) T_o\left(1-\frac ag\right)
(C) T_o\left(1+\frac ag\right)
(D) T_o\left(\frac ag-1\right)

Solution
At Equilibrium (Rest), Free body diagram of block

T_0+mg=F_{up}
T_o+V\rho_Sg=\;\;V\rho_Lg\\
Vg(\;\rho_L-\;\rho_S)\;=T_o
\rho_L-\;\rho_S=\frac{T_o}{Vg}\;-----(1)
Free body diagram of block when it moves upwards.

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