The outer diameter of a hollow cylindrical iron rod is 8.4 cm. The rod is 28 mm thick and is 30 cm long. If the weight of 1 cm³ of iron in the rod is 0.5 kg, then find the total weight of the rod.
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Correct answer: D
Explanation
Given:
Outer diameter = 8.4 cm
Thickness = 28 mm = 2.8 cm
Length = 30 cm
Weight of 1 cm³ of iron = 0.5 kg
According to the formula:
Volume of a hollow cylinder = πh(R² − r²)
Outer radius R = 8.4/2 = 4.2 cm
Inner radius r = 4.2 − 2.8 = 1.4 cm
Volume = π × 30 × (4.2² − 1.4²)
= π × 30 × (17.64 − 1.96)
= π × 30 × 15.68
= 1478.4 × 0.5
= 739.2 kg