A roller used to flatten a cricket pitch has radius 0.7 m and length (height) 2 m. Find the area covered in one complete revolution (its curved surface area). Use π = 722.
Class 8MensurationMensuration
A17.6
B8.8
C9.8
D7.8
Step-by-Step Solution
Area in one revolution = CSA = 2πrh =2×722×0.7×2=2×22×0.1×2=8.8m2.
Answer: B) 8.8
Key idea: Surface area and volume of a cylinder
A cylinder is a circle stacked vertically. Two measurements: radius r and height h.
**Curved surface area (CSA) = 2πrh** (imagine 'unrolling' the curved surface — it becomes a rectangle of width 2πr and height h).
**Total surface area (TSA) = 2πr2+2πrh=2πr(r+h)** (curved surface + two circular ends).
**Volume = πr2h** (area of circular base × height).
Use π = 22/7 when r is a multiple of 7; otherwise π ≈ 3.14.
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