Q.The height of a right circular cone is twice the length of its radius. If the height were 7 times the base diameter, the volume of the cone would be 539 cubic cm more. Find the height of the cone.

Let the radius of the right circular cone be \( r \) cm So, the base diameter of the cone = \( 2r \) cm ∴ Height of the cone \( h = 2r \) cm ∴ Current volume of the cone = \[ \frac{1}{3}\pi r^2 h = \frac{1}{3}\pi r^2 \times 2r = \frac{2}{3}\pi r^3 \text{ cubic cm} \] Now, if the height were 7 times the base diameter, then height = \( 2r \times 7 = 14r \) cm ∴ New volume = \[ \frac{1}{3}\pi r^2 \times 14r = \frac{14}{3}\pi r^3 \text{ cubic cm} \] According to the question: \[ \frac{14}{3}\pi r^3 - \frac{2}{3}\pi r^3 = 539 \Rightarrow \frac{12}{3}\pi r^3 = 539 \Rightarrow \frac{12}{3} \times \frac{22}{7} r^3 = 539 \Rightarrow r^3 = \frac{49 \times 7}{2 \times 4} = \frac{343}{8} \Rightarrow r = \frac{7}{2} \] ∴ Height of the cone = \( 2r = 2 \times \frac{7}{2} = 7 \) cm
Similar Questions