A block of iron has dimensions 2 m x 0.5 m x 0.25 m. The density of iron is 7.8 g cm^-3. Find the mass of the block.

Density of iron = 7.8 g cm^-3
1 g cm^-3 = 1000 kg m^-3
7.8 g cm^-3 = 7.8 x 1000 = 7800 kg m^-3

Volume of iron = 2 m x 0.5 m x 0.25 m = 0.25 m³

Mass = ?

$\text{Density} = \dfrac{\text{Mass}}{\text{Volume}} \\[1em] \text{7800} = \dfrac{\text{Mass}}{\text{0.25}} \\[1em] \text{Mass} = 7800 \times 0.25 = 1950 \text{kg}$

So, mass of iron = 1950 kg.