2018 · Q78
A semi-circular plate is rolled up to form a conical surface. The angle between the generator and the axis of the cone is
Elementary MathematicsMensuration
- A60°
- B45°
- C30°
- D15°
Explanation
Rolling the semicircle of radius R into a cone: the slant height is R, and 2 pi r = pi R gives the cone's base radius r = R/2. The sine of the angle between the generator and the axis is r/R = 1/2. So the angle is 30 degrees. Hence option C.