Concrete ring

The concrete ring (used for reinforcement in wells) has an inner diameter of 800 mm and an outer diameter of 900 mm. It is made of concrete with a density of 2,500 kg/m³. Its height is 1 m. Calculate its mass.

Final Answer:

m =  333.7942 kg

Step-by-step explanation:

$$\begin{gathered} d=800\text{mm}\to \text{m}=800:1000\text{m}=0.8\text{m} \\ D=900\text{mm}\to \text{m}=900:1000\text{m}=0.9\text{m} \\ \rho =2500{\text{kg/m}}^3 \\ h=1\text{m} \\ {r}_1=d/2=0.8/2=\frac{2}{5}=0.4\text{m} \\ {r}_2=D/2=0.9/2=\frac{9}{20}=0.45\text{m} \\ {S}_1=\pi \cdot r_1^2=3.1416\cdot 0.4^2\doteq 0.5027{\text{m}}^2 \\ {S}_2=\pi \cdot r_2^2=3.1416\cdot 0.45^2\doteq 0.6362{\text{m}}^2 \\ S=S_2-S_1=0.6362-0.5027\doteq 0.1335{\text{m}}^2 \\ V=h\cdot S=1\cdot 0.1335\doteq 0.1335{\text{m}}^3 \\ m=\rho \cdot V=2500\cdot 0.1335=333.7942\text{kg} \end{gathered}$$

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