Height ratio for equal volumes (cylinder vs cone): A right cylinder and a right circular cone have the same radius and the same volume. Find the ratio of the height of the cylinder to the height of the cone.
Aptitude
Volume and Surface Area
Difficulty: Easy
Choose an option
-
A3 : 5
-
B2 : 5
-
C3 : 1
-
D1 : 3
Answer
Correct Answer: 1 : 3
Explanation
Introduction / Context:With the same radius, equal volumes force a relationship between heights using V_cyl = π r^2 h_c and V_cone = (1/3) π r^2 h_k. Equate and solve for h_c : h_k.
Given Data / Assumptions:
- Same radius r; equal volumes.
- V_cyl = π r^2 h_c, V_cone = (1/3) π r^2 h_k.
Concept / Approach:
- Set π r^2 h_c = (1/3) π r^2 h_k ⇒ h_c = h_k / 3.
Step-by-Step Solution:
h_c = (1/3) h_k ⇒ h_c : h_k = 1 : 3.Verification / Alternative check:
Pick r=1, h_k=3: V_cone=(1/3)π*1*3=π; with h_c=1, V_cyl=π.Why Other Options Are Wrong:
- 3:1 / 3:5 / 2:5: Inconsistent with the cone’s 1/3 volume factor.
Common Pitfalls:
- Inverting the ratio (writing 3:1 rather than 1:3).
Final Answer:
1 : 3