Steel tube

The steel tube has an inner diameter of 4 cm and an outer diameter of 4.8 cm. The density of the steel is 7800 kg/m³. Calculate its length if it weighs 15 kg.

Correct answer:

l =  3.478 m

Step-by-step explanation:

$$\begin{gathered} D_1=4\text{cm}\to \text{m}=4:100\text{m}=0.04\text{m} \\ {D}_2=4.8\text{cm}\to \text{m}=4.8:100\text{m}=0.048\text{m} \\ {r}_1=D_1/2=0.04/2=\frac{1}{50}=0.02\text{m} \\ {r}_2=D_2/2=0.048/2=\frac{3}{125}=0.024\text{m} \\ S=\pi \cdot r_2^2-\pi \cdot r_1^2=3.1416\cdot 0.024^2-3.1416\cdot 0.02^2\doteq 0.0006{\text{m}}^2 \\ m=15\text{kg} \\ h=7800{\text{kg/m}}^3 \\ V=m/h=15/7800=\frac{1}{520}\doteq 0.0019{\text{m}}^3 \\ l=V/S=0.0019/0.0006=3.478\text{m} \end{gathered}$$

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