Class 8 Surface Area of a Cylinder — practice questions with answers
Mensuration · 5 sample questions from the school syllabus. Try each one, then open the answer and the worked solution.
1. Which formula gives the curved surface area of a cylinder with base radius r and height h?
Aπr²h
B2πrh
Cπrh
D2πr(r + h)
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Answer: B) 2πrh
Unrolled, the curved surface is a rectangle of length 2πr (the base circumference) and breadth h, so its area is 2πrh. πr²h is the volume, and 2πr(r + h) is the total surface area.
2. Using π = 3.14, find the curved surface area of a cylinder with radius 10 cm and height 5 cm.
A628 sq cm
B1570 sq cm
C314 sq cm
D157 sq cm
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Answer: C) 314 sq cm
CSA = 2 × 3.14 × 10 × 5 = 314 sq cm. 157 forgets the 2; 1570 is the volume πr²h.
3. If the radius of a cylinder is doubled and its height is halved, what happens to its curved surface area?
AIt doubles
BIt stays the same
CIt halves
DIt becomes 4 times
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Answer: B) It stays the same
New CSA = 2π(2r)(h/2) = 2πrh. The doubling and the halving cancel out.
4. A cylinder has radius 7 cm and height 7 cm. What is the ratio of its curved surface area to its total surface area?
5. A closed cylindrical petrol tank lies on its side. It is 5 m long with diameter 1.4 m. Painting its whole outer surface costs ₹30 per sq m. Find the cost. (Take π = 722.)
A₹706.20
B₹660
C₹1504.80
D₹752.40
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Answer: D) ₹752.40
r = 0.7 m. TSA = 2 × 722 × 0.7 × (0.7 + 5) = 4.4 × 5.7 = 25.08 sq m. Cost = 25.08 × 30 = ₹752.40. ₹660 paints only the curved part; ₹706.20 includes one end.