Q: A cubical block of wood of edge a and density ρ floats in water of density 2ρ . The lower surface of the cube just touches the free end of a mass less spring of force constant k fixed at the bottom of the vessel. The weight W put over the block so that it is completely immersed in water without wetting the weight is

(a) $ \displaystyle a(a^2 \rho g + k) $

(b) $ \displaystyle a(a \rho g + 2k) $

(c) $ \displaystyle a( \frac{a \rho g}{2} + 2k) $

(d) $ \displaystyle a(a^2 \rho g + \frac{k}{2}) $

Ans: (d)