A cylinder of circumference 8cm and length 21 cm rolls without sliding for 4 ½ seconds at the rate of 9.

Complete rounds per second. Find the area covered by the cylinder in 4 ½ seconds.

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1350

2500

6804

7804

answer is C.

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Detailed Solution

We have cylinder with circumference 8 cm and length 21 cm.
Number of round per second = 9
Number of round in 4 ½ secons = 4 ½ x9 = 81/2
Circumference of cylinder = 8 cm
2⊼r= 8 cm
r=8/2⊼
Curved surface area of cylinder = 2xrh
= 2x22/7 x 8/2⊼ x 21 = 168 cm2 Area curved in 1 round = curved surface area
Area curved in 81/2 rounds = 81/2 x curved surface area
= 81/2 x 168 = 6804 cm2 Hence, option 3 is correct.

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