The GATE Grind

GATE 2017 ME (ME1) – Question 3

General Aptitude · Quantitative Aptitude: Algebra, Geometry and Mensuration · 1 mark · Multiple choice

A right circular cone of base radius 5 cm and height 12 cm is rolled on the ground while its apex P stays fixed, until the marked base point Q touches the ground again. Through what angle in radians about P does it travel?

Diagram for GATE 2017 ME (ME1) question 3
  1. $5\pi/12$
  2. $5\pi/24$
  3. $24\pi/5$
  4. $10\pi/13$

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (D) $10\pi/13$

Explanation

The slant height is $s=\sqrt{5^2+12^2}=13$ cm. Unrolling the lateral cone surface gives a sector of radius 13 cm and arc length equal to the base circumference $2\pi(5)=10\pi$ cm. The sector angle is arc length divided by radius, $\theta=10\pi/13$ radians. Rolling once until Q returns to the ground sweeps this angle about the fixed apex, giving D.

More Quantitative Aptitude: Algebra, Geometry and Mensuration questions

All Quantitative Aptitude: Algebra, Geometry and Mensuration questions →