A right circular cone of circular base radius R and H resting on a plane. The cone is cut by a plane parallel to the base. The new circular cone-formed has a 12.5% volume of the older cone. What is the height of the new cone?
A right circular cone of circular base radius R and H resting on a plane. The cone is cut by a plane parallel to the base. The new circular cone-formed has a 12.5% volume of the older cone. What is the height of the new cone? Correct Answer h = H/2
Calculation:
Let r and h be the radius and height of the new cone.
Volume of new cone = (1/3) × π × r2 × h
⇒ 12.5% of the volume of the old cone
⇒ (1/8) × (1/3) × π × R2 × H ---(1)
Also, since the new cone created from the old cone.
⇒ r/h = R/H
⇒ r = Rh/H
∴ Volume of new cone = (1/3) × π × (Rh/H)2 × h
⇒ (1/3) × π × (R2/H2) × h3 ---(2)
Using (1) and (2)
⇒ H3/8 = h3
⇒ h = H/2
Additional Information
The surface area of a circular cone = πr(l + r) where l is the slant height and r is the radius of the circular base.