A steel pipe is 300 cm long with an outer radius of 10 cm and an inner radius of 8 cm. How many kg does this steel pipe weigh? (the weight of steel per cubic centimeter is 7.8G, and the number obtained will be kept to two decimal places)

A steel pipe is 300 cm long with an outer radius of 10 cm and an inner radius of 8 cm. How many kg does this steel pipe weigh? (the weight of steel per cubic centimeter is 7.8G, and the number obtained will be kept to two decimal places)

Bottom area of steel pipe: 3.14 × 102-3.14 × 82, = 314-200.96, = 113.04 (square centimeter), volume of steel pipe: 113.04 × 300 = 33912 (cubic centimeter), weight of steel pipe: 33912 × 7.8, = 264513.6 (g), = 264.5136 (kg), ≈ 264.51 (kg); answer: this steel pipe weighs about 264.51 kg

An annular steel pipe has an inner radius of 4cm, an outer radius of 5cm and a height of 8cm. Its volume is () cubic centimeter
As mentioned above-

Volume = (3.14 × 5-178; - 3.14 × 4-178;) × 8
=3.14×(5²-4)²×8
=3.14×9×8
=226.08 (cm3)
A: its volume is (226.08) cubic centimeter

A rectangular wooden block is 12 cm long, 10 cm wide and 8 cm high. What is the volume of the cuboid?

Volume = 12 × 10 × 8 = 960 CC