A mass of 120g half immersed in water displaced a volume of 20cm³. Calculate the density of the object.

Since the object is half immersed and displaces 20 cm³, its total volume is twice the displaced volume.

$$V_{object} = 2 \times V_{displaced}$$ $$V_{object} = 2 \times 20 \text{ cm}^3 = 40 \text{ cm}^3$$

$$\rho_{object} = \frac{m_{object}}{V_{object}}$$ $$\rho_{object} = \frac{120 \text{ g}}{40 \text{ cm}^3}$$ $$\rho_{object} = 3 \text{ g/cm}^3$$

The density of the object is $\text{3 g/cm}^3$.