Shortcut Trick
For a cylinder, CSA2 = 4π2r2h2 = 4π(πr2h)h = 4π(V × h), which gives a direct relation: CSA ∝ √(V × h).
⇒ CSA1 / CSA2 = √(V1h1 / V2h2)
⇒ Ratio = √[(√2 / √3) × (4 / 9)]
⇒ Ratio = √[(21/2 × 22) / (31/2 × 32)] = √(25/2 / 35/2)
∴ The correct answer is 25/4 : 35/4.
Alternate Method
Given:
Ratio of Volumes, V1 : V2 = √2 : √3
Ratio of Heights, h1 : h2 = 4 : 9
Formula Used:
Volume of Cylinder (V) = πr2h
Curved Surface Area (CSA) = 2πrh
Calculations:
⇒ V1 / V2 = (πr12h1) / (πr22h2)
⇒ √2 / √3 = (r1 / r2)2 × (4 / 9)
⇒ (r1 / r2)2 = (√2 / √3) × (9 / 4)
⇒ (r1 / r2)2 = (21/2 × 32) / (31/2 × 22)
⇒ (r1 / r2)2 = 33/2 / 23/2
⇒ r1 / r2 = (3 / 2)3/4 = 33/4 / 23/4
Now, substitute these derived ratios in the respective CSA relation formula:
⇒ CSA1 / CSA2 = (2πr1h1) / (2πr2h2)
⇒ CSA1 / CSA2 = (r1 / r2) × (h1 / h2)
⇒ CSA1 / CSA2 = (33/4 / 23/4) × (4 / 9)
⇒ CSA1 / CSA2 = (33/4 / 23/4) × (22 / 32)
⇒ CSA1 / CSA2 = 22 − 3/4 / 32 − 3/4
⇒ CSA1 / CSA2 = 25/4 / 35/4
∴ The correct answer is 25/4 : 35/4.
Additional Information
Total Surface Area of Cylinder
The total surface area encompasses both the curved surface and the two flat circular bases, calculated using TSA = 2πr(r + h).
Volume and CSA Relation
The volume of a cylinder is V = πr2h and CSA = 2πrh. Squaring the CSA directly proves the relation: CSA2 = 4π(V × h).
Cone Formulas
For a cone having a radius r and standard height h, the curved surface area is CSA = πrl (where l = √(r2 + h2)) and Volume = (1/3)πr2h.