Multiple choice

The area of the base of a right circular cone is $28.26\;sq.m$. If its height be $4\;m$, find its curved surface. (Take $\pi=3.14$)

  1. $47.1\;m^2$
  2. $42\;m^2$
  3. $48.8\;m^2$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Base area = pi * r^2 = 28.26. r^2 = 28.26 / 3.14 = 9, so r = 3. Height h = 4. Slant height l = sqrt(r^2 + h^2) = sqrt(9 + 16) = 5. Curved surface area = pi * r * l = 3.14 * 3 * 5 = 47.1.

AI explanation

Using the base area formula pi*r^2, we find the radius by solving 28.26 = 3.14 * r^2, which gives r^2 = 9 and r = 3 m. Applying the Pythagorean theorem, the slant height l is sqrt(3^2 + 4^2) = 5 m. The curved surface area is pi*r*l, so 3.14 * 3 * 5 = 47.1 square meters.

Keep practicing — related questions