Volume of log of wood $V = \frac{\text{mass}}{\text{density}} = \frac{120}{600}$ =0.2 m 3

Let x weight that can be put on the log of wood.

So weight of the body = $(120 + x) \times 10 \, \mathrm{N}$

Weight of displaced liquid = $V \sigma g = 0.2 \times 10^{3} \times 10 \, \mathrm{N}$

The body will just sink in liquid if the weight of the body will be equal to the weight of displaced liquid.

∴ ∴ $(120 + x) \times 10 = 0.2 \times 10^{3} \times 10$

$\Rightarrow \quad 120 + x = 200$ ∴ ∴ x = 80 kg