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The ratio of the radius of the base to the height of a cylinder is 3:1. If its volume is 9702 cm3, then the curved surface area of the cylinder is: (Use π=722)
616 cm2
946 cm2
668 cm2
924 cm2
924 cm2
Express radius and height as 3x and 1x. Substitute into the volume formula to find x³, solve for x, then directly compute the curved surface area using the values of r and h.
Ratio of base radius to height of a cylinder (r : h) = 3 : 1. Cylinder volume V = 9702 cm³. Use π = 22/7.
V=πr2h and CSA=2πrh
Express radius and height as 3x and 1x. Substitute into the volume formula to find x³, solve for x, then directly compute the curved surface area using the values of r and h.
Students often forget to find the cube root of the constant or confuse the radius (r) with the diameter in the formula.
Define dimensions
Given the ratio r:h=3:1, let r=3x and h=x.
r=3x,h=x
Solve for x
Substitute r and h into the volume formula V=πr2h=9702. So, 722×(3x)2×x=9702. Thus, 722×9x3=9702. Solving for x3: x3=22×99702×7=343. So, x=3343=7.
x=7
Calculate dimensions
Since x=7, the radius r=3×7=21 cm and height h=7 cm.
r=21,h=7
Calculate CSA
The curved surface area is CSA=2πrh=2×722×21×7.
CSA=2×22×3×7=924
D is correct because the calculated curved surface area is 924 cm².
This problem uses algebraic substitution common in both 3D Mensuration and ratio-based arithmetic questions.