Multiple choice

A right triangle with sides 3 cm, 4 cm and 5 cm is revolved about the side 3cm to form a cone. Which of these is false?

  1. Curved surface of cone =20π

  2. Total surface area = 36π

  3. Volume=(80 /3)π

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

Revolving a 3-4-5 triangle about the 3cm side creates a cone with height h=3, radius r=4, and slant height l=5. Curved surface area = pi*r*l = pi*4*5 = 20*pi. Total surface area = pi*r*l + pi*r^2 = 20*pi + 16*pi = 36*pi. Volume = (1/3)*pi*r^2*h = (1/3)*pi*16*3 = 16*pi. Option C claims volume is 80/3*pi, which is false.

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