Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section A

Chapter

Applications of Derivatives

Question:

The height of the cylinder of maximum volume which can be inscribed in a sphere of radius r is:

Options:

$\sqrt{3}r$

$r/\sqrt{3}$

$2r/\sqrt{3}$

$r/2\sqrt{3}$

Correct Answer:

$2r/\sqrt{3}$

Explanation:

Let h be the height, x be the base radius, and V be the volume of the cylinder.

$∴r^2=x^2+h^2/4$

$V=πx^2h=πh(r^2-h^2/4)=πr^2h-πh^3/4⇒dV/dh=πr^2-3πh^2/4$

Now $dV/dh=0⇒πr^2-3πh^2/4=0⇒4r^2=3h^2⇒h=2r/\sqrt{3}$