In a right circular cylinder, the ratio of curved surface area to total surface area is 1 : 2. If the total surface area is 616 cm^2, find the volume of the cylinder.

Difficulty: Medium

Correct Answer: 1078 cm3

Explanation:


Introduction / Context:
We are given a relationship between curved surface area (CSA) and total surface area (TSA) for a cylinder and its TSA value. From the ratio, we deduce a relation between radius and height, then compute volume.


Given Data / Assumptions:

  • CSA : TSA = 1 : 2.
  • TSA = 616 cm^2.
  • Standard formulas apply.


Concept / Approach:

  • CSA = 2πrh.
  • TSA = CSA + 2πr^2 = 2πrh + 2πr^2.
  • Given TSA = 2 * CSA ⇒ 2πrh + 2πr^2 = 4πrh ⇒ r = h.
  • With r = h, TSA = 4πr^2 ⇒ solve for r.
  • Volume V = πr^2h = πr^3 with h = r.


Step-by-Step Solution:

4πr^2 = 616 ⇒ r^2 = 616 / (4π)Take π = 22/7 ⇒ 4π = 88/7 ⇒ r^2 = 616 * 7 / 88 = 49 ⇒ r = 7 cmh = r = 7 cm ⇒ V = πr^2h = (22/7)*49*7 = 22*49 = 1078 cm^3


Verification / Alternative check:
Compute CSA = 2πrh = 2*(22/7)*7*7 = 308 cm^2; TSA = 616 cm^2 satisfies the 1:2 ratio exactly.


Why Other Options Are Wrong:

  • 1632, 1232, 1848 cm^3: Do not follow from the r = h constraint with the given TSA.
  • None of these: Not applicable since 1078 cm^3 is exact.


Common Pitfalls:

  • Misapplying the TSA formula (forgetting the two bases).
  • Not reducing the ratio properly to r = h.


Final Answer:
1078 cm^3

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