Question : A hollow cylindrical tube made of plastic is 3 cm thick. If the external diameter is 20 cm and the length of the tube is 49 cm, find the volume of the plastic.
Option 1: 7238 cm3
Option 2: 7644 cm3
Option 3: 7546 cm3
Option 4: 7854 cm3
Correct Answer: 7854 cm 3
Solution :
External Radius = $\frac{20}{2}$ = 10 cm
The internal diameter of the tube can be found by subtracting twice the thickness from the external diameter.
Internal diameter = 20 – 6 = 14 cm
Inner Radius = $\frac{14}{2}$ = 7 cm
The volume of the plastic can be found by subtracting the volume of the hollow portion from the volume of the entire cylinder:
Volume of the plastic = $\pi (R^2-r^2)h=\frac{22}{7}\times(10^2-7^2)\times49= 7854$ cm
3
Hence the correct answer is 7,854 cm
3
.
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