Iron rod

What is the mass of a cylindrical iron rod with a length a = 9 m and a diameter d = 6 cm? The density of iron is 7,800 kg/m³.
Express the result in kilograms, and round to the nearest whole number.

Correct answer:

m =  198 kg

Step-by-step explanation:

$$\begin{gathered} a=9\text{m} \\ d=6\text{cm}\to \text{m}=6:100\text{m}=0.06\text{m} \\ \rho =7800{\text{kg/m}}^3 \\ {S}_1=\pi \cdot (d/2{)}^2=3.1416\cdot (0.06/2{)}^2\doteq 0.0028{\text{m}}^2 \\ V=S_1\cdot a=0.0028\cdot 9\doteq 0.0254{\text{m}}^3 \\ m=\rho \cdot V=7800\cdot 0.0254=198\text{kg} \end{gathered}$$

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